Bandmaster Reverb TFL5005D Is this a circuit designation?

[Michael Smith]

I have been studying Bandmaster Reverb schematics in anticipation of potentially buying one. The amps I have seen online from around 1968 to the early 1970's have TFL5005D printed on the front panel under "Fender Bandmaster". The schematics I have found online (EL World) are AA 568, AA 1069 and AA 270. Bothe the AA 1069 and AA 270 schematics have TFL5005D typed right under the main schematic title and in the "Drawing Title" box in the bottom right corner. The schematic for the AA 568 does not have any reference to TFL5005D, but that circuit revision is the odd and short lived hybrid cathode and fixed bias version and uses a different power transformer.

So does anyone know what the TFL5005D refers to? The Wiki article on the Bandmaster Reverb lists TFL5005D as a circuit revision, but I kind of doubt that. The Wiki article also fails to mention the AA 270 circuit revision. I've yet to compare 1069 to 270 to see what if any differences in component values there are.

[phantomman]

The first Bandmaster Reverb I ever saw was in the fall of 1968 when two were delivered to our store. I asked our senior tech about the circuit and he described it as an AB568 Super Reverb with the O/T swapped for that of a Pro Reverb. Comparing the schematics, that was precisely what it appeared like to me. I would assume the geneology of the BMR roughly paralleled that of the SR during the production life of both models.

[Michael Smith]

Ya, all of the amps in Fender's lineup in that era shared a very similar circuit design. Here is a photo of one, purportedly from 1971 with TFL5005D printed under the amp name (kind of hard to see), but it's there.



I think you're right Phantomman. I compared the AA1069 schematics for the Super Reverb and the Bandmaster Reverb, and the only difference I could find was the output transformer. So the Bandmaster Reverb is a Super Reverb in a head cabinet. I guess the biggest risk in buying one is that you would get the AA568 circuit with the ill-fated hybrid bias circuit (and different power transformer with higher voltages throughout). It would be pretty easy to spot the 150ohm 7 watt resistors on the cathodes of the power tubes, but most online sellers aren't providing pictures of the inside of the chassis.

[Michael Smith]

I may have answered my own question after a little more searching. "TFL5005D = Domestic Fender Bandmaster Reverb
TFL5005X = Export Fender Bandmaster Reverb"

So it's not a circuit revision designation. Apparently the Dual Showman Reverbs from this era had a similar designation.


The TFL may refer to Teflon wire covering according to one forum post I found.

[phantomman]

The TFL may refer to Teflon wire covering according to one forum post I found.

I'd heard that as well.

[Michael Smith]

I wouldn't pay top dollar for a Bandmaster Reverb head, since I already have a 1969 Super Reverb in very good condition which I serviced last year, but if I could find one in poor condition it would be nice to fix up and see how it sounds thru my 4 x 10" 4 ohm speaker cabinet and compare it to the Super Reverb. I haven't tinkered around inside an old Fender chassis since last fall.

[phantomman]

The BMR starts to compress and distort much more quickly than a SR due to the BMR's smaller output iron. They're actually good candidates for conversion to an AB763 Vibroverb clone.

[Michael Smith]

The BMR starts to compress and distort much more quickly than a SR due to the BMR's smaller output iron. They're actually good candidates for conversion to an AB763 Vibroverb clone.

I'll have to look into that. I actually prefer an amp that doesn't break up too early. Thankfully there are plenty of schematics available online. If I got one cheap enough, I wouldn't mind tinkering with it.

[Cogs]

I own a TFL5005D that I converted into a 2x10" combo. It sounds absolutely incredible & I get remarks on it nearly every time I play out with it. I call it my "Baby Twin"

[Michael Smith]

I own a TFL5005D that I converted into a 2x10" combo. It sounds absolutely incredible & I get remarks on it nearly every time I play out with it. I call it my "Baby Twin"

Sweet! So in effect you have 1/2 of a Super Reverb. I don't know if you saw the comments earlier, but the circuit for the Bandmaster Reverb and Super Reverb are identical, except for the impedance of the output transformer. Makes me want to find a "fix-er upper" even more.

[phantomman]

The SR's O/T is half again as large as a BMR's. It's almost as big as a Showman's.

[Michael Smith]

The SR's O/T is half again as large as a BMR's. It's almost as big as a Showman's.

So I guess that means that you would have to keep the BMR's speaker impedance as close as possible to 4 ohms. I always try to match the speaker cab impedance to the schematic specs, even though some of the O/T's can handle a mismatch.

I have one that I have made a serious inquiry on, hoping it's not the AA768 circuit.

[Cogs]

I was told that the chassis & knob arrays for the BMR & SR are identical.

[phantomman]

I was told that the chassis & knob arrays for the BMR & SR are identical.

Correct. The same chassis in modified form is also used for the Bassman 10.

[Michael Smith]

Well, I purchased the 1969 Bandmaster Reverb. All original condition, so I will have some work to do. I'll start a new thread with photos once it arrives. Sadly, it has the AA768 circuit, so I guess I'm stuck with that. I don't think I could convert it to AA1069 with the power transformer it has (unless it is a transitional model with the "newer" transformer. I doubt it). The circuits are virtually identical, except for the cathode resistors, although the voltages differ quite a bit.

[phantomman]

My records indicate that all BMR's prior to the ultra-linear version use the same power transformer, Fender P/N 022798.

[Michael Smith]

My records indicate that all BMR's prior to the ultra-linear version use the same power transformer, Fender P/N 022798.

Hmm the schematics I looked at showed 125P70 for the AA769 circuit, and 125P50 for the AA1069 and AA270 circuits. What else would account for the voltage differences at various locations, since all resistor values appear to be the same? I guess I'll have to see which power transformer mine has when it arrives.

Edit: Perhaps it's the different rectifier tube.

[phantomman]

I've got an AA768 archived but no AA769. P/N 125P7D is a non-reverb Bandmaster P/T.

[Michael Smith]

I've got an AA768 archived but no AA769. P/N 125P7D is a non-reverb Bandmaster P/T.

Ya, the AA769 is a typo. I meant AA768. I have a list somewhere on my computer cross referencing all of the common transformers. I'll have to look for it tomorrow. Perhaps that is a "D" rather than a "0" on the schematic I found. Not the clearest image. Or the schematic could be incorrect.

[phantomman]

P/N 125P7D is correct. That same tranny is used in the brownface Pro Amp. Curiously, the part number translates to 022814 under FMI's parts list but I cannot find any evidence that the part was ever used in any CBS-era amp.

[Michael Smith]

The Fender transformer number conversion chart (see link) indicates the same transformer was used in all 3 non-ultralinear Bandmaster Reverb circuit revisions, namely 125P5D. https://el34world.com/charts/transch...more%20rows%20.

However, this schematic for the AA768 circuit shows the 125P7D power transformer was used.

I can confirm that my AC568 Bassman amp uses the 125P7D (Fender part no F022814) power transformer. I took the chassis out of the cabinet this morning to make a note of all of the transformer part numbers, something I should have done with my other amps when I had them apart for servicing.

I guess I will have to see which power transformer my Bandmaster Reverb has when it arrives. I do know that it has the 150 ohm 7 watt cathode to ground resistors, as the seller sent me some photos of the inside of the chassis.

Edit: And to further complicate things, here is a BMR AA768 schematic that shows a GZ34 rectifier tube. It doesn't show which power transformer was used.

[phantomman]

The 5U4GB replaced the GZ34 in the AA1069 revision.

I think you might be surprised (pleasantly) with the tone of the AA768 circuit.

[Michael Smith]

The 5U4GB replaced the GZ34 in the AA1069 revision.

I think you might be surprised (pleasantly) with the tone of the AA768 circuit.

I hope so! I have an article comparing the GZ34 to the 5U4GB rectifier tubes. I'll have to dig it out and read it again. From what I recall the 2 tubes draw different amounts of current. Depending on which transformer mine has, I will use the appropriate rectifier. I know some people say the 2 rectifiers are interchangeable, but I believe that is dependent on the power transformer.

I think I like researching the amp circuits and doing the servicing as much as I like playing through them.

[phantomman]

Yeah, the heater-current draw is substantially higher with the 5U4GB by 50%. Regardless, the GZ34 always seemed to provide more sag when the amp was driven hard.

[Cogs]

Well this ought to clear things up:

[Cogs]

Just kidding. This is the actual tube chart that is in my '72 BMR. Pretty sure it's an AA1069 though

[Michael Smith]

I have found the Fender tube charts to be very inaccurate. My Bassman with an AC568 circuit has an AB 165 tube chart. At least the tubes listed are correct. (diode rectifier, so there's no confusion around a rectifier tube.) I'll be tracing my circuit carefully when my BMR arrives, and hopefully chose the proper rectifier tube.

[phantomman]

Post-1967 Fender tube charts should be relied on only for tube type and placement.

[Michael Smith]

Well, my 1969 BMR arrived today. It's definitely the AA768 Circuit with the 150 Ohm 7 watt resistors between the cathodes of the power tubes and ground. Oddly it has the 125P5D Power Transformer, Not the 125P7D as shown on the AA768 schematic. Mine also came with a 5U4GB rectifier, not the GZ34 shown on the schematic. The rectifier is a GE, so it may be the original. All other tubes are JJ's Tung-Sol or Sovteks. So my amp may have been a transitional circuit, or they just used whichever power transformer they had on hand. The tube chart specifies a GZ34 rectifier, not that that means anything.

I'll post pictures, probably in a new thread when I get done testing it. My multi-meter isn't measuring resistance accurately, so I'll need a new one.

[phantomman]

We'll need an audio assessment as well.

[Michael Smith]

We'll need an audio assessment as well.

I'll try to post something on YT. I'll have to blow the dust off my Pro Tools rig, lol. I did install the tubes and played thru the normal and "vibrato" channels. Vibrato and reverb worked fine and the channels were dead quiet, except for a little popping when I turned it off and left it the standby "on" to discharge the caps. Probably some leaky caps. The main filter caps in the doghouse all dated to 1969. Surprised they aren't showing any signs of leaking electrolytic fluid, although I will do a full service on the amp before using it too much. It does have a grounded power cord and a Sprague 100/100 bias cap, but I don't see any other signs of anyone working on it, which is good so I won't have to troubleshoot mistakes.