1973 pro reverb - weird wiring?

[Warrenghall]

Good day

for those knowledgeable in fender amp schematics I think I’ve got a weird one. I recently purchased a stock 1973 pro reverb. It currently play well and sounds good - although occasionally the volume fluctuates. I figure the first step is recap as it is till has all originals. When I opened it up I found a few things I found weird - and could not related back to the schematic1. In the filter cap can there should be 2 220 k resistors. In mine I seem to have 1 220 k and the other seems to be 300 ohms. Haven’t been able to find any schematics where bothe resistors aren’t 220 k’. Should I change them to be both 220 k as part of the

2 when I look at the main board there are typically three double 25/25 capacitors in the middle of the board, which are replaced by 6 25/50 during the recap. I don’t have these. The first on the left has 2 original capcitors, while all the rest of the spots just have a single 25/25. Again - have never seen this on a schematic. Also - as these are not paper caps do I still need to change them or should I let well enough Be?

[Michael Smith]

I have only seen 220k resistors used as balancing resistors for the first filter stage. They are intended to divide the voltage equally going to the reservoir caps (70uF/350Volts). Note the polarity of these two capacitors, they are wired in series. As for the dropping resistors for the rest of filter stages, I have seen variations in the values used over the different circuit revisions. AA1069 uses a 1K followed by a 4.7K. AA270 uses a 2.2K followed by a 10K. (the dropping resistors are often hidden under the filter caps, so you will need to remove the filter caps to see the values).

As for whether the remaining electrolytic cathode bypass caps on the eyelet board are the "double" 25/25's or individual 25/25's, it probably depended on what they had in stock at the time. My preference is to change out these caps as well as the bias cap and resistor when doing service on one of these amps. You can find recap kits online that come with all of the doghouse and eyelet board caps and some resistors. You may want to check the values of all of the resistors in the circuit and order any needed replacements at the same time. Some techs replace the screen resistors on the power tubes as a matter of course, whether they measure OK or not.

Edit: The schematics specify using 1Watt resistors in the filter cap board (doghouse). There is no harm going to 2Watt carbon film or metal oxide resistors here. Also, upping the value of the bias capacitor is often done.