Ampeg Reverberocket II- GS-12R - Caps and Power section?

[goldenmonkeycolor]

*** I thought this was going to be posted a response to a previous thread, but it made its own new topic. Hopefully that's okay!

FLiptops is making the tremolo module again!!! SO now I'm back into the amp. I realized I just didnt understand speaker cabinet mounting hardware and I dont need to get at the front of the bolts since they're like t nuts or whatever that stay in place in the front of the cabinet.

I've got some questions regarding the capacitors and cap can situation in my amp. It appears to me that the cap can only provides 70uf? I have three filter caps inside my chassis that are all connected to the cap can terminals. One of them actually connects to two cap can terminals the other two are just grounded there apparently. The other gold one goes to the power tubes, the red one connects to a resistor on the control panel side of the tagboard then grounds at the cap can terminal.

Anyways- the gold caps are 20uf 450v. and the big red cap is 40uf 450v. I canty make sense of this when the cap can says 70uf 30uf 20uf. Shouldnt it be taking care of all of capacitors need in the amp?

I'm also wondering what type of power section is in this amp? Is it cathode biased or fixed bias? How could I measure the plate dissipation and adjust the bias? Is it the 1k resistors going to each power tube?

I know i'm a newb but I can work safely in amps and have revamped several fenders completely (because there is so much step by step instructions for fenders). I cant afford a tech at the moment so any help will be repaid in good karma forever and perfect blue checker tolex on all future ampeg pawn shop finds!

[Stevem]

These amps are famous for having the power transformer short out when those stock 4 section filter cans start to go, no less with the level of burned up stuff you have in that amp!

In light of this I would prove out that your PT is good first before you move on and here is how to do that!

First unsolder all the wire from the secondary side of the PT.
Next get a 1 ohm 5 to 10 watt resistor and solder in inline to the non PT side of the amps fuse.

Hook you meter up across this resistor and set it for low AC volts and turn the amp on making sure all of your secondary wire will not short on something, if you find that the meter is reading more than .4 volts you have a bad PT, a shorted PT will read 1 to 2 volts ,if not than the repair can move on!

Those two gold colored can caps where added to Gin up that failing multi section can cap and this is a old old TV repair way for getting something back up and running, but your still left with a rotting hot running stock filter mounted in the amp !

Antique electronics has the multi section type caps you need to replace that and they cost some 40 bucks, also replace all the electrolytic caps through out the amp while you are at it and replace that SS bridge recto also while you are at it since it was likely pushed to its limit also!

While you are at it the output tube cathode resistor can be kicked up to 15 watter to help keep the bias on the output tubes more stable when things are reved up and singing!

When you first power the amp up after the repair, do so with all the tubes out and a 1/2 amp fast blow type fuse in place, if that holds then you are likely golden to load in the right fuse and all the tubes and play away!

Oh, also the on / off switches in these amps get pretty flaky with age and I have had a few of those smoke up at times also!

[Leo_Gnardo]

Antique electronics has the multi section type caps you need to replace that and they cost some 40 bucks, also replace all the electrolytic caps through out the amp while you are at it and replace that SS bridge recto also while you are at it since it was likely pushed to its limit also!

I would be wary of those CE caps. Not only expensive, but I've tried em, had 'em fail fast, and so have too many others. Antique has lots of good things and excellent service but their multisection caps, well they look good, that's about all.

In Ampegs and similar amps that had multisections, I sub in 50+50 uF 500v caps aimed at the Marshall market. You can get 'em F+T, JJ, or Ruby labeled, current brands that have proven to work well. They need a bracket to mount but no worries - the holes in the chassis already fit that bracket no drilling necessary. Replace the other sections with individual caps. Cost of the whole kit, 50+50, bracket, 2 single caps, will likely add up to less than the CE. Also no need to worry over "inexact" cap values compared to original - the 50+50 has worked perfectly well in every repair I've done with it.

[goldenmonkeycolor]

So... Sorry I didnt make this point clear. The amp is working, sounding good, great even. It doesnt sound fantastic when it's cranked up though. The tremolo circuit isnt working, but ive narrowed it down to needing the 'bug' replaced.

Regarding the caps, So those gold caps are just there instead of the cap can? How do you know when a cap is "failing" like starting to fail but still working? especially a specific part of a multi cap?

I guess I really dont care for spending a lot of money on multi section caps. I'm having trouble relating the schematic to the capacitors that are actually in the amp. Understand what I'm saying? I'd be perfectly happy replacing the cap can with axial indivudal caps inside the chassis. But I dont know how to go about doing that when I feel like the schematic is making me misunderstand whats happening in the amp! Like I do feel like I could follow the schematic and install capacitors based on what I see in the schematic, but this cap can

[Leo_Gnardo]

Regarding the caps, So those gold caps are just there instead of the cap can? How do you know when a cap is "failing" like starting to fail but still working? especially a specific part of a multi cap?

Looks more like somebody added extra filter caps to act as "helpers" perhaps to an inadequate or failing multisection cap. We'll have to have a more detailed close up shot of that corner of the chassis to really tell what's what.

Failing filter caps: current starts passing through the capacitor, increasing hum, reducing hi voltage available to the amps' tubes, and heating the cap from the inside out. Carried to completion, there's a breakdown point where crud starts leaking out the end of the capacitor, and it may start drawing so much current that it wrecks the power transformer. You can pretty well count on filter caps to last 20-25 years unless they're in a spot they're being baked, then less. At 50 years or so, like in your amp, it's almost a sure thing, should replace original caps as necessary preventive maintenance. Keep a good thing going.

Consider the 50+50 cap, two main cap sections will be outside the chassis so you'll have less of a task placing the remaining sections inside.

[Mach Schnell]

If the current rating for the fuse is calculated properly, there should never be a pt meltdown, circuit protection 101....

[sluckey]

If the current rating for the fuse is calculated properly, there should never be a pt meltdown, circuit protection 101....

If it can go wrong, it will, Murphy's Law #1...