Very low output on '65 Ampeg Reverberocket R12-R-T

[drasp]

Just traded my YBA-1 for a '65 Reverberocket, wanted something smaller than my other amps (Bassman, HIWATT, JC120) w/ onboard trem & 'verb & the Ampeg seemed to really fit the bill. Plus, finding a local friend who had one & was willing to swap was icing on the cake!

At the friends house, I plugged into the Ampeg & noticed that not only was the output low, but there was a ton of noise. Once I got it home, 30min w/ some DeOxit sorted the noise & it idles fairly quiet now, but unfortunately w/ the volume DIMED the output is lower than a Champ & has little headroom.

Before I just start randomly replacing tubes & caps, I wanted to post this problem here & see if I could get some insight!

Here are some gut shots:













And HERE is a link to the schematic.

I'm pretty much a total noob as far as trouble shooting like this goes, but I've done cap jobs, 3-prong conversions, replaced obviously damaged components, etc. Also happy to take any measurements that can be done w/ a DMM. . .

Thanks in advance for any help!!!

[Chuck H]

Some voltage tests could be helpful. Unless that reveals something obvious I would plug in some known good power tubes and new filter caps before anything else.

Chuck

PS good trade!

[drasp]

Some voltage tests could be helpful. Unless that reveals something obvious I would plug in some known good power tubes and new filter caps before anything else.

Chuck

PS good trade!

Thanks Chuck. I've got this up on another, smaller forum where a few very knowledgeable dudes reside & they're suggesting the same.

Over the years I've fallen into the bad habit of leaving as much original on my amps in possible, out of some baseless fear that I'll strip them of their 'something'. Obviously, I'm not going to get away with it on this one. . . I'll report back as progress is made.

[drasp]

Replaced the filter caps on either end of the chassis w/ a pair of 20uf 500V Atoms. No change on the volume (not surprised) but they were all that I could find locally.

All the caps for the power supply are in the cap can, which is a 60/40/10/20 µF @ 450V - not going to be an easy one to find in a direct match.

Looking at AES, my options appear to be using something with higher values (80/40/30/20 µF @ 475 VDC is one option) or something like a 40/40/20/20 µF @ 525 VDC & mess around w/ combining caps (40+20 to get the 60) and adding one outside the can. . .

[txstrat]

To find out if the issue is preamp or power amp related I usually desolder the wire before the PI and clip the wire to a known good power amp.
If the headroom is still very low the problem is probably in the preamp (provided the power amps are roughly the same wattage).
You could also clip a preamp signal from another amp into the Ampegs power amp (before the PI) and see if the other amps preamp is low on headroom as well. Then the issue is probably in the Ampegs power amp.
This sort of troubleshooting is way easier when you have an effects loop but works with clipped leads as well.
Just my 2c

[g1]

Speaker has been verified as good, yes? (just making sure)

[ParthaD]

Try replacing just those 2 blue caps...

... hey just came across those amazing pics! I just LOVE ampegs! Been working with a whole fleet of them, cannot believe the ridiculous prices that people just about give them away for these days when they develop problems! But sshhhh!

Anyway, working on both SS and tube amps (unmodified) from that era, on testing the caps I've found a very high occurance of caps from that particular maker failing, from Silvertones to Ampegs.

YMMV of course!

Good luck!

[Alex R]

Your caps may well be bad but they are not the number one suspect - I'd say check the tubes first. Given the rarity of some of these types it might be worth finding someone with a tube tester rather than investing in a whole new set.

About your output tubes - I note that Sovtek/EH have manufactured a 7868. My experiences with such small-run rare-type modern manufacture tubes has not been universally good, though I have not tried these particular tubes - worth asking around on here before making a purchase at what I see are relatively high prices.

[Rich]

I'm trying to trace out a similar amp; different tubes, roach type tremolo. The schematic is damaged but there is enough left to show me there is nothing like it online so I've got to trace things out to make my own layout drawing, then I can work out a schematic.

The 3 polypropylene caps on the extreme left are replacements, maybe they have an issue.

In the cap can, the 20uf section is 25v and hooks to the v6 cathode so it can be replaced outside the can somewhere on the wire going to v6.

When I finish my trace job, I'm going to remove the cap can with a view of removing the guts and stuffing replacement caps inside.

[Dave Curtis, dB AudioTech]

"About your output tubes - I note that Sovtek/EH have manufactured a 7868. My experiences with such small-run rare-type modern manufacture tubes has not been universally good, though I have not tried these particular tubes - worth asking around on here before making a purchase at what I see are relatively high prices."

I have used them, and while they sound pretty much the same as the originals, the pins are bigger than the old ones (unless they've changed). I thought I was going to break the sockets getting them in. Of course, if you want to use the old ones after you stuff the EH ones in there, you'll have to retension the sockets or they'll fall out.

I know looks can be deceiving, but the 7868s in that amp look like they haven't had a hard life (no obvious signs of overheating, the glass near the plate vents is nice & clear, etc). I have some that look much worse that still work well.

[1ampman]

You need to check all the voltages on the tube sockets and power supply. After you find the problem, it also needs all the electrolytics and many film caps replaced, and some resistors. These parts are past their end of their lives..... I've repaired several Ampegs and the original caps don't hold up.

[Rich]

The schematic pasted inside the back cover of my amp, though damaged, does show the nominal voltage at the plates; good starting place and easy to check if you still have it in your amp.

[Dave Curtis, dB AudioTech]

You need to check all the voltages on the tube sockets and power supply. After you find the problem, it also needs all the electrolytics and many film caps replaced, and some resistors. These parts are past their end of their lives..... I've repaired several Ampegs and the original caps don't hold up.

One of these days I plan on replacing the (38 year-old) 'lytics, but all the components in my VT22 are original (and measure good), and that amp still kicks ass. BTW, film caps and resistors don't have a "lifespan". Measure and replace if out of spec. Electrolytic caps are a different story.