Fender Pro Reverb

[makjoh]

I'm trying to figure out which circuit applies to my 1973 Fender Pro Reverb. It has the 5U4GB rectifier but only 5 bypass capacitors on the board with another one wired to a pre amp tube and the reverb input (6 in total) they are all 25uf/25volt with the exception of one being 5uf/50volt. All the circuits seem to mention 7 capacitors on the board and all 25uf/25 volt ??

[tdvt]

Try this one.

This has a MV but I think otherwise fits your description. There may be a non-MV version out there.
 

https://el34world.com/charts/Schematics/files/Fender/Fender_cbs_45w_mstrvol_pullsw_super_pro_bmstr_rev_2_.pdf

[sluckey]

Why do you need to know? Just curious or is the amp broke? A good tech should be able to fix any Pro Reverb using any of the Pro Reverb schematics.

Fender made some undocumented changes to the Pro Reverb amps. The AA1009 and AA1069 are the only ones that show a 5U4 and a 5µF bypass cap in the tremolo circuit. But both these models have a total of 7 bypass caps.

Can you show some hi-rez pics of the inside of your amp? We may be able to determine which bypass cap is missing on your amp.

[sluckey]

Try this one.

Yes, this is probably it.

[makjoh]

Why do you need to know? Just curious or is the amp broke? A good tech should be able to fix any Pro Reverb using any of the Pro Reverb schematics.

Fender made some undocumented changes to the Pro Reverb amps. The AA1009 and AA1069 are the only ones that show a 5U4 and a 5µF bypass cap in the tremolo circuit. But both these models have a total of 7 bypass caps.

Can you show some hi-rez pics of the inside of your amp? We may be able to determine which bypass cap is missing on your amp.

Well the amp was sounding shite  I've replaced the filter caps (popped and leaking) and bypass caps which were the old white Mallory caps. I was just looking at the schematics and layouts for Pro Reverbs and all of them had the two extra caps. Just wondering if a previous tech had removed them for whatever reason.....whoever it was installed a lineout/headphone socket (with some resistors) on the front of the amp by drilling through the P in Pro Reverb, it's then wired to come off the speaker outs.I don't like it and intend removing it. The tubes were fine except the P.I. tube which was replaced. It's working and sounding like it should now. So yeah, I'm curious about those potential missing caps that are present in the schematics

[sluckey]

So yeah, I'm curious about those potential missing caps that are present in the schematics

Well, put them in your amp. Ain't gonna hurt anything.

[tdvt]

Too bad about the extra hole in the faceplate. Fender added a line-out on the late 70's UL version, so maybe someone was trying to update yours, back in the day.

The schematic I linked earlier didn't have a bypass cap on the reverb driver, which explains the lower count.

Sounds like you have it already sorted, but out of curiosity, is yours the early MV version?

[makjoh]

Too bad about the extra hole in the faceplate. Fender added a line-out on the late 70's UL version, so maybe someone was trying to update yours, back in the day.

The schematic I linked earlier didn't have a bypass cap on the reverb driver, which explains the lower count.

Sounds like you have it already sorted, but out of curiosity, is yours the early MV version?

I don't think it was a master volume model, unless a previous owner has removed the components and utilised the hole for its current purpose. But the faceplate would have been different, nah, he's drilled through the P and created this lineout. I'll get some pics attached as soon as I can. The 6 th cap is actually connected between the tube and vibrato not the reverb, my mistake

[sluckey]

The 6 th cap is actually connected between the tube and vibrato not the reverb, my mistake

It's most likely connected to the convenient ground lug of the vibrato FS jack.

[makjoh]

The 6 th cap is actually connected between the tube and vibrato not the reverb, my mistake

It's most likely connected to the convenient groutnd lug of the vibrato FS jack.

Yes, correct, that's where it's connected. I've got the amp on the bench again because those lovely clean chimey tones on volume 3 with a strat were starting to lose volume, sounding flat and quiet until I hit the strings hard where it seemed to make a slight popping noise and kick back into life. I thought it might be a bad earth on cable or guitar, but they test fine on a different amp. The problem was a continual one so I'm re checking everything. Unless you gents have experienced something similar and can pin point a particular area?

[Esquirefreak]

Possibly a power tube going bad.

/Max

[makjoh]

Possibly a power tube going bad.

/Max

Tubes are fine, test good in another amp. I'm picking up some unusual readings at the coupling caps that connect to the PI tube... 393 vdc on the 1st cap 243 vdc on the second cap. Schematic states 260 vdc for both. I've rebiased the amp and took further measurements. Everything seems fine apart from those caps which are settled at 300 vdc

[tubeswell]

Could be a cold solder joint on one of the connections you replaced. Reflow with some solder and flux

[makjoh]

Could be a cold solder joint on one of the connections you replaced. Reflow with some solder and flux

Its definitely on the board. The board has warped over the years and when pressing down on one of the warps with a chopstick I can make the problem go away. I can hear the intermittent connection somewhere around the tone stack caps. I'll re solder every connection and see if it cures it. If not then I have a little winter project of stripping the board and installing a new board