Custom Vibrolux Reverb - Mark Moyer Mods

Look into thread "Custom Vibrolux breakup", post made by stjohn1299 on 1/17/2008. There are several other comments about the CVR in general, tube changes, etc. Mark Moyer is quite the AR amp inquisitor...;-)

I ordered everything today to do every mod I have seen, as well as to put it all back together as original. Had to order another style of 3300pf cap, but I'll search for the Silver Mica between now and the time I expect to hotwire this thing...

Take a pic of the speaker pos (+) grounding when you get to that NFB loop mod. The 470 ohm resistor to ground probably will appear obvious once I take things apart...but a pic of your mod would make it much more clear. It is the only mod that seems the printed wiring board is lacking a convenient spot to secure that lead.

It's not caused by mod #1 then.

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Originally Posted by Kap'n

It's not caused by mod #1 then.

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OK, do you have any ideas of how I could troubleshoot this? Have you seen anything similar before?

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Originally Posted by twangmeisternyc

Look into thread "Custom Vibrolux breakup", post made by stjohn1299 on 1/17/2008. There are several other comments about the CVR in general, tube changes, etc. Mark Moyer is quite the AR amp inquisitor...;-)

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Not able to find that post or the user (weird)? Can you send a link?

http://www.fenderforum.com/forum.htm..._number=658307

hi. first of all i want to say that i am spanish and that my english is not as good as it used to be as i don't use it very much now. so if i misunderstand something or i don't explain something in a logical way just let me know and i will try again.

i don't know a thing about electronics. no more than that i can read here and in tubestore.com, etc so i just make trial-error process and let my ears to judge. i use 5751 in the bright channel because is the channel i use and the 5751 allows me to push the volume a bit more. i don't use normal channel at all. i did some tests in V6 with 6201's and several 12AT7 i have, including current production sovteks and a couple of NOS RCA and GE. it always ended with hum(with NOS RCA and GE, and sovteks) and very loud hum when using original GT (sovtek) 12AX7. hum just dissapeared when using NOS GE 6201. when i bought the amp it came with a Electroharmonix 12AX7 in V3. i replaced it with another 6201 and put the EH(as far as i know this tube has great output for the average of 12AX7) in V4. i think it works pushing the reverb a bit but i think i will end doing these mark moyer mods as i need more reverb to do some of the tones (think parker and lily - the low lows) i am in now. i need to say that i also have a twin reverb i love its tone and reverb but it has too much wattage for the clubs i usually play.

hey fezzy, would you post some pics of the pcb with the mods done. also it would be nice some pics of the NFL, just for reference.
if anyone following this topic has a 63 vibroverb reissue, would you post some pics of the pcb? thanks!

Your english is just fine surfcaster...as well as your ears!

When I swapped in/out AT's for AX's across the sockets I never really noticed hiss reduction, but I surely felt the gain/volume change. Could well be the NOS GE's and EH's are just inherently quiet. And from what I have seen for NOS prices...quite addictive!

I've been chatting here and on another board about the CVR...many folks don't seem to have an issue with idle hiss, or don't care, etc.

But now that we know we can start tweaking around... ;-)

As Nigel Tufnel says, "This one goes to 11"

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Originally Posted by surfcaster

hey fezzy, would you post some pics of the pcb with the mods done. also it would be nice some pics of the NFL, just for reference.
if anyone following this topic has a 63 vibroverb reissue, would you post some pics of the pcb? thanks!

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No problem. I'll take some pictures this weekend and post them to this forum.

I'd very much like to see a schematic or even some pics of the 63' Vibroverb RI if anyone out there has either.

http://www.schematicheaven.com/fende...6g16_schem.pdf

I found this schematic...maybe it helps.

Regards

That appears to be the super old vibroverb schematic. We are hoping to find the 63 re-issue schematic. For some reason its really hard to find... non of the schematic sites I've run across seem to have it either.

I guess I thought maybe we could figure something out with the old schematic, a component value or a wire connection. I searched around for the RI schematic for about half and hour. Only other thing I found was a guy on EBay who converts 63 RI's back to real BF. Nice website, been doing amp stuff for 10 years. You send him your amp chassis, he sends you back a real '63. I bet he has a schematic. I'll call him later this morning.

Stu-Daddy Amps (586) 777-1338 Warren, Michigan

http://www.stu-daddyamps.com/servlet/StoreFront

I called, he has both the schematic and PWB layout, and says he won't share or copy anything. Oh, well, such is life...

I pulled the chassis out this morning...everything I see to do is straight forward...no biggie. I just need to get my desoldering/soldering "chops" back in gear.

The NFB loop description was worded a bit goofy, but now having seen it, Mark is just describing that a jumper-wire-to-ground is currently in the slot at R42 and needs to be replaced with a 470 ohm resistor (I assume this as I have not turned the board over, yet, to trace the Pt2 circuit path to R42 then to a common ground).

When I first read the process for the NFB mod it seemed there was a real plastic coated wire running from somewhere to somewhere, or one needed to add such a wire, plus I think he uses "vibroverb" incorrectly when what he means to say is "the pcb board" common to both our CVR and the Vibroverb.

My mind kept laughing once I looked at everything as if one of those movie scenes where they are defusing a bomb, only to get the next instruction about "going back" or "not forgetting to" after they snipped the wrong wire!

Fezzy,

I have 100 ohm resistors in positions R62 and R63. Did you buy your CVR "new", or is there a chance someone before you replaced yours to 47 ohm? Maybe Fender just had one of those "specs to change w/o notice" days at the factory with a 100 ohm shortage...

Additionally, mine came with a 2-spring reverb pan, a "4"-series Accutronics. Mark describes his as a 3-spring "9"-series. It has a bit more impedance, but would also be a lot fuller. Surfcaster might consider that since he is seeking more reverb. Using Mark's Reverb Driver mod (AX tube vs. AT) would provide more push, too.

Once I get everything, I'll start the mod's...

First, the Footswitch ground change.
Second, the Tube changes. I ordered Jan-Philips 5751 for V1, V2.
Third, the Reverb cap.
Fourth, the Ground Reference resistors.
Fifth, the Shunting Cap on the Phase Inverter.
Sixth, the Surge Diodes.

Once I see how much headroom I gain from the tube changes I'll review the NFB loop change.

And, ...if I still ponder life on this planet as to why I hear hiss...I'll consider separating the two channels for BRIGHT only reverb.

And, after all the above, if I get REVERB hallucinations I'll change my tank to a "9" series, and go for the 12AX7 mod!

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Originally Posted by twangmeisternyc

Fezzy,

I have 100 ohm resistors in positions R62 and R63. Did you buy your CVR "new", or is there a chance someone before you replaced yours to 47 ohm? Maybe Fender just had one of those "specs to change w/o notice" days at the factory with a 100 ohm shortage...

Additionally, mine came with a 2-spring reverb pan, a "4"-series Accutronics. Mark describes his as a 3-spring "9"-series. It has a bit more impedance, but would also be a lot fuller. Surfcaster might consider that since he is seeking more reverb. Using Mark's Reverb Driver mod (AX tube vs. AT) would provide more push, too.

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Yes, I got my amp new from the factory. I'll take a look at R62 & R63 and test them again to see what I get. It is possible that it could have been a goof or a deliberate change at Fender. Who knows.

Oh, and some of Marks writings confused me too... just the way stuff was worded I guess. But it all made sense once I got to look at the PCB. :)

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Originally Posted by twangmeisternyc

Additionally, mine came with a 2-spring reverb pan, a "4"-series Accutronics. Mark describes his as a 3-spring "9"-series. It has a bit more impedance, but would also be a lot fuller. Surfcaster might consider that since he is seeking more reverb.

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i haven't checked the reverb tank. i will do it next rehearsal. thanks for the advice!

Surfcaster,

$28.50 @www.MojoMusicalSupply.com - for the 3 spring long delay tank...less than one of those fancy tubes you are using! ;-)

Not sure what the gain is on a 6201 (60%?), but a Sovtek 5751 (70%) might give you some boost as a V3 reverb driver. Surely, the Reverb cap mod is a half-way point to add some more tone.

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Originally Posted by twangmeisternyc

Only other thing I found was a guy on EBay who converts 63 RI's back to real BF. Nice website, been doing amp stuff for 10 years. You send him your amp chassis, he sends you back a real '63. I bet he has a schematic.

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The '63 is the Brown Vibroverb, which the RIs are based off of. Converting it to BF is the '64, and then you've gone from bias modulating tremolo to the BF optoisolator tremolo. There are other small differences throughout, mostly in component values throughout the circuit.

I bet he's a licensed Fender tech and can't share the schematics by nature of his contract with Fender.

It's pretty direct of a job to put in a handwired circuit to replace the PCB in amps like this...the '65 reissues (Deluxe, Super, Vibrolux, and Twin) are prime candidates as well.

I'd do it in a heartbeat if I came into one of these.

My tubes and parts have shipped...amp is disassembled, chassis upside down with 15" speaker baffle plugged in, leaning against the wall. I really want to go through these tube changes first. Last time I did it, I used Sovtek 5751's and the JJ/Tesla ECC81's in the pre-amp slots. What I read, however, is "short plate" 5751's or 6201's are just inherently quiet (made for hi-fi ap's), with the Sovtek 5751 being better used elsewhere than the pre-amp. It's a well-made rugged tube, probably best as the reverb driver. The ECC81's I'll slip into the phase inverter. Currently, have Sovtek 6L6WXT+ for power tubes, and I have a pair of matched Winged C's 6L6 standing by...

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Originally Posted by twangmeisternyc

Surfcaster,

$28.50 @www.MojoMusicalSupply.com - for the 3 spring long delay tank...less than one of those fancy tubes you are using! ;-)

Not sure what the gain is on a 6201 (60%?), but a Sovtek 5751 (70%) might give you some boost as a V3 reverb driver. Surely, the Reverb cap mod is a half-way point to add some more tone.

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no no no... believe me 28.5$ is more than i usually pay for a preamp tube. if i don't remember badly i paid 15-20€ for 5 NOS 6201. Last tube i have bought :

http://cgi.ebay.es/ws/eBayISAPI.dll?...m=310007722515

IMO you don't have to pay lots of money for "matched 12AX7's" or "superclean logos" etc. i think this things are for collectors. what i do is have 2 or 3 trustful sellers, and be patient. when the tube arrives i take it to my tech for testing. sometimes a tube is bad, but in the global result it is a nice and cheap way to find tubes. since today i have had good luck... cross fingers!

Just an update...

You can get a CVR Service Manual @

http://www.schematicheaven.com/fende...lux_manual.pdf

And the 63 Vibroverb Owner's Manual @

http://media.musicalplanet.com/pdf/FEN302.PDF


In the parts list it describes component types and values. I made a mistake or two ordering my parts... but for mods I do not plan to do at first. Mainly on types of components..type of resistor, type of capacitor, etc. Look that document over well. Check wattage and voltage, etc. Also, R23 is listed on the Parts List at 18k ohms, ...but in my unit it is 47k ohm. R23, which takes both pre-amp tube anodes to ground, is also listed as METAL OXIDE type, 1 Watt. R37, in the NFB loop circuit, is listed as "FILM", not following the code, so, maybe it was supposed to be METAL FILM, 1 Watt. In my unit R23 and R37 look essentially the same, METAL OXIDE type. As a comment, if R23 were at 18k ohms, this pre-amp would have run REAL HOT!

Second, the Fender folks emailed me a '63 Vibroverb Reissue schematic and layout drawing. I thought they would want me to send a $10 check and letter as described on the website Support section...but I've had email and phone chats with them in the past regarding past and future purchases, I am probably in the database...nice gesture on their part.

Third, initial review of the 63 Vibroverb has the Reverb Cap, C16 listed as 3300pf (.0033uf) 400V. On the CVR parts list, this component is a 500pF, 1000V ceramic disc type, not a Silver Mica. I think Ceramic Disc is fine here as that Silver Mica is tough to find.

I am pondering whether one must change to BRIGHT ONLY Reverb to switch to the .0033uF capacitor for it to have full benefit. The circuit changes seem to be independent enough of that capacitor change, one 1/2W 220K ohm (R11) resistor going to 300V "X", the other, R35, 1/4W 220k ohm connecting the NORMAL channel back into the circuit ahead of the phase inverter. Both are a long way from the Reverb circuit mechanics. Would be nice to have someone else chime in on that question. Also, I think a value somewhere in between 500pF and 3300pF might be just fine if the effect is too much.

Fourth, the C20 shunting capacitor on the 63VV schematic is listed as 100pF, 1000V.

Fifth, The C11 BRIGHT channel filter cap @ 47pF, Ceramic Disc, 1000V is also a bit of an oddity in the marketplace should you wish to order a spare.

Sixth, the footswitch grounding scheme change must be from other older Fender amps...the CVR and 63 VV are the same on the schematic.

Seventh, over on the other forum, someone just had several of the mods completed and thought they were great.

http://www.fenderforum.com/forum.htm..._number=661747

Finally, I received my JAN-Philips 5751 tubes today, more on those soon.

I started the mod's yesterday...

First, let me say if I get yet another cut on a finger or thumb from struggling with getting the chassis out, I probably will need to give up guitar playing... ;-)

Lots of burrs all over, ... a bit surprised by that. Additionally, lots of hang-ups with the tolex and RF foil under the top panel board.

I went through a long series of tube changes. Where I ended up was V1,V2 Jan-Philips 5751, V3 Sovtek 5751, V4 Tungsol 12AX7, V5 the original Fender GT 12AX7, V6 JJ/Tesla ECC81, and V7, V8 Sovtek 6L6WXT+. As a final comment about doing the tubes, those Jan-Philips 5751's were almost impossible to get in, really buggers...

Where in the past when I de-gained the pre-amp with the Sovtek 5751 or the JJ/Tesla ECC81's, and did not notice much idle hiss reduction...I'd say the Jan-Phillips did give a proportional noise improvement. Also, adding the JJ/Telsa on the phase inverter helped again. Using the Sovtek 5751 for the Reverb Driver added a lot more than it's gain difference. Reverb really perked up. I would also say my Vibrato sounded better, not so much the chugging - more the smooth swirling.

My Jensen C15N speaker baffle is a lot deeper and a lot brighter than the original Jensen 2-10 Alnicos. I'd say BRIGHT channel using the Alnico's might even be less than the NORMAL channel with the Ceramic 15. Reverb on the C15N was actually very good, especially when perpendicular to the unit. In such a small apartment space, when directly in front of the unit I think the reverb cancels out, just the geometry of the walls makes it feel faint.

When it came time to make the footswitch ground mod, I was using the 2-10 Alnicos. I snipped the gray wire, leaving about a 1/4 inch, stripped and tinned the lead, and then secured it to V4 pin 2 along with the green wire. Not a big deal. I did notice that the popping when depressing the footswitches was less noticeable, I wouldn't say the pop had disappeared.

I did, however, get into a bit of Reverb Feedback during that session, most likely due to the placement of the loose tank in the unit, the effect of the Alnicos,... lots of potential reasons. In any case I could not go over 7.5, where before I could go to 10. I need to put the C15N baffle back in to see if the effect is recreated. I doubt the footswitch mod had a thing to do with it unless that 1/4" piece of wire I left standing became a super transmitter antennae.

I also had torn out a fair amount of the RF foil which I repaired with several layers aluminum foil and clear 3M high quality packing tape. I trimmed out and the reglued any unworthy tolex that was snagging the chassis, too. Sliding the chassis back in was much easier.

I received my components...and as expected a few of the resistors I'll need to reorder.

More as it happens...

I did a bit more today, switching speakers, tubes, etc. I mounted the reverb tank properly, ran the cables better, etc. Still having a bit of a reverb squeal as I approach "10". It came and went a bit, too. There were times "10" was fine.

My power here today was pretty terrible, we get a recurring buzz/transient fairly regularly that I have never figured out. It affects our phone, too...quite audible. Not sure if it is the building, pumps/fans/equipment cycling on and off, or if it is straight from ConEd. Maybe that is as much of it as anything else.

I would describe the Vibrato footswitch pop as being less, and now maybe the Reverb footswitch pop is equal where before it was negligible.

I plan to switch the footswitch ground back as original, and see what that does...

My notes are underlined and bold below:

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Originally Posted by twangmeisternyc

Second, the Fender folks emailed me a '63 Vibroverb Reissue schematic and layout drawing. I thought they would want me to send a $10 check and letter as described on the website Support section...but I've had email and phone chats with them in the past regarding past and future purchases, I am probably in the database...nice gesture on their part.
Could you send me a copy of the 63 Vibroverb Reissue schematic?? I'd love to see it.

Third, initial review of the 63 Vibroverb has the Reverb Cap, C16 listed as 3300pf (.0033uf) 400V. On the CVR parts list, this component is a 500pF, 1000V ceramic disc type, not a Silver Mica. I think Ceramic Disc is fine here as that Silver Mica is tough to find.
The idea behind using a Silver Mica is that it will sound better. Try both, you will probably notice a big difference.

Silver Mica 33pf

Fourth, the C20 shunting capacitor on the 63VV schematic is listed as 100pF, 1000V.
I don't think it matters. Someone else mentioned that its not likely to have 1000v running anywhere through this amp. 500v should be fine. Has worked for me so far.

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Quote:

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Originally Posted by twangmeisternyc

I did a bit more today, switching speakers, tubes, etc. I mounted the reverb tank properly, ran the cables better, etc. Still having a bit of a reverb squeal as I approach "10". It came and went a bit, too. There were times "10" was fine.

My power here today was pretty terrible, we get a recurring buzz/transient fairly regularly that I have never figured out. It affects our phone, too...quite audible. Not sure if it is the building, pumps/fans/equipment cycling on and off, or if it is straight from ConEd. Maybe that is as much of it as anything else.

I would describe the Vibrato footswitch pop as being less, and now maybe the Reverb footswitch pop is equal where before it was negligible.

I plan to switch the footswitch ground back as original, and see what that does...

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I switched my footswitch ground back to the PCB connection. I think the CVR that Mark Moyer worked on was an early model (1995-97) and had some slight differences from the CVRs being built now.

Check your Silver Mica info, it's .0033uF (3300pf). Right now I have a Ceramic disc and an Orange Drop to try. When I went looking, only Cornell Dubilier made a Silver Mica at that 3300pf, and the only places to purchase were more main line OEM suppliers with $300 minimum buys. It was also a non-stocked item. I'll keep looking.

And, those higher Voltage ratings are just a safety factor. Some caps get really pounded...just like the Reverb Driver tube gets pounded.

Also, I found a link that described designing solid-state reverb circuits, and in the article it gives a range of cap values. Right now, the CVR is 500pf, which is a low value by similar measures. This article describes 1500 to 10000pf (once you do the math), as the working range.

http://sound.westhost.com/project34.htm

Lower values give that Classic Fender booming Reverb sound. Higher values are supposed to give an added "shimmer" like Stevie Ray Vaughn.

The .0033uF (3300pF) is in the lower of that working range, and is common to a lot of Fender spring reverb amps.

I'll switch the ground on the footswitch back and give it a another listen. I think the schematics are probably correct. Both are the same, and Mark's note describes his scheme as being from "earlier Reverb" amps.

My issue as delivered with the CVR was if I left Reverb on, and switched off Vibrato, I got a fairly noticeable pop. If I turned reverb off first, not so much. The mod is a pop either way, just less noticeable.

Oops, yeah I looked at that wrong. Here is the actual cap that I used to replace the ceramic disc in C16:

Orange Drop .0033uf

I hear orange drop caps are known for their great tone. However, I have no idea if they are preferred for use in a reverb circuit. Either way it sounds great to me and it hasnt blown up or anything.... yet. :)

Orange Drops are used a lot,...they start to have issues at very high frequencies. Silver Mica are the most suitable. Ceramic do high frequencies well, but drift, vary, etc. more so than the other two.


http://thetubestore.com/parts.html

These folks have values either side of that 3300pf. Nice guys, I order my tubes there.

Deleted, added above

Interesting. I may order a few different ones and try them out.

I returned the footswitch ground back to the printed circuit board, and it seems the reverb feedback issue is better, more tolerant. I did everything without plugging in a guitar, but I did enough switching and swapping and plugging and unplugging yesterday to say without all that the factory grounding scheme may be a bit more stable.

There is more resistance to ground going to the V4 pin2, it is fixed/static, but in the factory scheme it passes through the REVERB potentiometer itself, and depending where one has it dialed up to, more so through the C16 capacitor. The pop in the mod is consistent, as one would expect it to be...in the factory scheme it varies depending on where the knob is set.

The REVERB pot is linear reverse, so when one dials higher it become less resistant, giving more reverb, and at maximum, there is both the pot and the 82k ohm resistor to ground for the footswitch. So, at the highest settings, the footswitch ground is completely through the pot.

Maybe the ground to the V4 pin2 is just more microphonic...

I'll give this all another go at some point.

As another footnote, I made no effort to put the tube holders over the tubes during all these tests, and I did have the 5751 in as the reverb driver. It has more gain. I was getting feedback yesterday with an AT7 so I do not think it was the critical path.

Also, when de-gaining the pre-amp with 5751 or ECC81's max volume is about 7, after that you begin to oversaturate the tube. The amp was designed to deliver more power than the 5751 or ECC81 can use.

i keep looking at this thread everyday as it is very interesting. i have no time now to do the mods as i am restoring a ruined SG that has been given to me. maybe i will start next week while i let the glue curing her neck.

anyway, and for the pop when disconnecting the tremolo, i remember mine had a very noticeable one. let me tell you that i had to convert my amp from 120V to the 230V we have in Spain. my tech did the new trafo and that pop was even louder! but he discovered that the 120V trafo had a capacitor embebed in the coil doing antiparasitics so he started playing with the values of the cap till most of the hum and the whole tremolo pop were dissapeared.

this afternoon i have been rehearsing with the amp... i love this amp men! i almost doubt it can improve with the mods... and i forgot to check the reverb tank! let see next thursday.

Just another update....

Been playing all my various guitars these past couple days. I really like the tube changes. Whether NORMAL or BRIGHT, 2-10 AlNiCo or 1-15 Ceramic, with or w/o REVERB or TREMELO...everything sounds better.

It's still the honeymoon, of course, but the de-gained pre-amp matched to the pumped up REVERB is great, and however/whatever with the de-gained phase inverter...the TREMELO just has that dreamy thing going on. I changed the Fender GT 12AX7 for a Tung-Sol as the Tube Oscillator when I was testing the Reverb Feedback on Sunday morning...so that is the only other change since those notes.

I need to grab a few tools this weekend to start working the other mods, I have them in storage at my father's house. Next is the Reverb Capacitor. This will be curious as the Reverb right now sounds pretty good.

I re-ordered the 82k, 47k, 39k, and 6.8k 1W MOS resistors, and along with ... some of those "addictive" NOS GE tubes, the 5751 and the 6201.

I have the footswitch ground back to factory schematic, no real issues if I remember to turn reverb off first before tremelo when both are on...

One last thing, there is an additional fuse on the PCB board not well listed on either the CVR schematic or parts list. It is a 5*20mm 10A 250V fast blow. Do your units have this fuse, too?

Yes, mine has that fuse too.

Could you give me a list of all the tubes you have tried at this point and up to your current setup? I'm ordering tubes tomorrow - currently using all of the original tubes except for V3 I have a mullard 12at7 nos that has worked out nicely.

As delivered it was all Fender GT, except as I recall, there was another AT7 in the Phase Inverter. I bought my unit "new", with a warranty, etc....but it was a special price, obviously a returned open box unit. My unit uses the WHITE bias GT 6L6B's and those were Sovtek 5881WXT production.

I bought a bunch of Tung Sol's 12AX7, the JJ/Tesla ECC81, and the Sovtek 5751 based on my internet searches, reading stuff, etc. Also, a bought a matched pair of the Sovtek 6L6WXT+ and the 6L6 Winged C's. All these tubes were for a point-to-point retro-fab Princeton Reverb high power amp I had ordered. However, I rejected it, sent it back...and had a pile of tubes!

For the CVR, I had been running Tung Sol's in both pre amps, the Fender AT7 for the Reverb Driver, then Fender AX7 through to the power tubes. I had the Sovtek WXT+ bottles I had ordered in for those, and those were screened for their bias at the vendor.

As I mentioned a while back...I've tried the JJ and the Sovtek 5751 as preamp tubes and reverb drivers, not sure I had ever used either for a phase inverter...

Now, thinking about, such a high gain pre-amp with those Tung Sol's would have been what I was hearing...an amp ready to SCREAM!

Right now, I have the Jan-Philips 5751 in for both preamps, a Sovtek 5751 in for the reverb driver, a Tung Sol AX7 in for reverb recovery and tremelo oscillator, and a JJ ECC81 in for the phase inverter. I have left the Sovtek WXT+ in for power tubes.

We need to keep in mind, once the NFB loop mod is done, the power to the pre amp tubes changes...so, the effect of de-gaining the front end will be different.

Hey Fezzy,

I re-read some of your earlier posts...it seems you changed the Reverb capacitor before separating the two channels. Did you notice any added hiss from doing that?

I think that 500pF value on the CVR was probably chosen to keep any added hiss (from having reverb in both channels, both channels wired together) from becoming a "sonic hiss machine". What do you recall?

Otherwise, that .0033uF cap is standard fair for lots of the 60's era spring reverb models...