Epiphone Century model 30 1956-57 amp

[Arhythmic]

Hello

I bought an old Epiphone Century 30 amp a couple of years ago, meaning to restore it and never got the time to do it... Now's the time!
It actually works, without any hum, buzz or hiss which never ceases to amaze me, but the output is extremely low. If I plug my guitar in any input (on both channels), I have to turn the volume pots way up and the sound becomes audible around 3 o'clock only.
My first suspicion were the tubes, so I replaced all of them with known-good ones and the result is strictly the same. Then I thought that is was maybe the sockets, cleaned them all carefully and still the output is very quiet. I also chopsticked the inside of the amp (both parts) for any loose soldering, still nothing...
I tried to find a schematic, but never did. Apparently, prior to Gibson buying Epiphone brand in 1958, a lot of Epiphone amps were made for them by Danelectro, so I looked up a for a similar Danelectro, late 50's schematic, and found quite similar ones, but not with my tubes array (2X 12AX7, 2X 6V6, 6SJ7, 6X5).
Have you seen this amplifier made by Danelectro? I saw a picture of it on a site once, but no model was specified.

Any suggestions are appreciated as I would really like to bring it back to (full) life again!

Thank you in advance!

[mozz]

Pots are date coded 4 so i take it 54'. Could be other numbers on the bigger caps, speaker and transformers.

[Enzo]

Stop guessing.

Looking at your innards, I will bet my lunch money ALL those wax covered caps are leaky, and need replacement. In fact the Astrons are likely paper caps too, and probably leaky. A simple test for this is to see how much DC leaks through them.

This is not a complex amp, sit down with paper and pencil and draw up a schematic from the circuit.

[Arhythmic]

Thank you gentlemen for replies!
Mozz, the codes on the pots and speaker suggest 1954 as a year of production, however I found an Epiphone 1954 catalogue and the Century model looks nothing like the one I have.
Enzo, you are absolutely right, replacing all capacitors will certainly fix the problem. Now, I really don't want to open that can of worms and start a debate of preservation vs. restoration (which is the cover topic of the Hemmings Classic Car magazine this month), but I would like to respectfully add that in my case I lean more towards preservation. I know, I know... I will never use this amp on stage, because I got less valuable, more robust and powerful amplifiers for that purpose. This amp is 63 years old and is in really good shape for its age and that's why I would prefer to not swap a 350SBC in it figuratively speaking, even if I will not obtain the full performance out it due to some less-than-optimal parts. I would really like to just address the most urgent problem for now: the low output. Also total absence of hum, hiss and buzz is also encouraging. I might also have to sell it eventually to finance some other ventures and I think that "mostly original" vs "totally rebuilt" will appeal more to the collectors who might take interest in this little amp. I have another Gibson (BR-6 from the early 50's) amp that will need a total rebuild, so I'm not against the idea at all, maybe just not in this particular case. That Epiphone is also a quite rare amplifier, so maybe preserving it in its original form will interest someone another 50-70 years later, even in non working form, which is not yet the case here. After all there are plenty of affordable and fully functionning substitutes out there.
Tracing a schematic is wonderful suggestion however!
Thank you again!

[mozz]

Here is the schematic. It may overload with a humbucker guitar. You may want to convert the grid leak bias on the input to regular cathode bias, if you don't know how to do that, get the amp working properly after a recap and we will walk you threw it.
https://el34world.com/charts/Schemat...ury30_1961.pdf

[Enzo]

I was implying that those old leaky caps ARE your problem. I am not suggesting replacing all those old paper caps just from age, I have rebuilt hundreds of amps from that era, including many jukebox amps, and the wax caps inevitably are leaky. Leaky caps upset the DC levels through the amp, and interfere with the signal path.

If you just want a museum piece, then wipe off the cab, and stick the thing on a shelf. If you want it to play, you are going to have to change parts.


What does Hemmings have to say about a 57 Chevy with fresh tires and a new battery?


Low output I can blame on caps. As to a lack of hum and hiss, well it the amp produces a very low output, you won't be able to hear any hiss it might have created.

You can always collect the dead caps as you remove them, and put them in a bag inside the amp, then any collector will have the old dead parts if he wants them.

[Enzo]

There you go, a schematic.

Look at the caps in circuit. Is there ANY DC at all on the bass pots? Shouldn't be. Any positive voltage on the grids of the power tubes? Shouldn't. How about the two 390k just right of the phase inverter, any DC on them?

[Arhythmic]

Thank you Mozz and Enzo! That schematic will certainly speed things up for me!
Enzo, thank you for suggestions, really. I hope I didn't come across as being disrespectful, I'm still a novice at best and I learn a lot from your and other members posts on this forum.
I think what is the missing link between the auto and audio industries is the availability of reproduction parts that wear out (tires, batteries, wipers, etc.) and that look OEM and period-correct.
I tried to look around for vintage-looking caps, but most of what I found is extremely expensive and seem very cork-sniffy... So, following your suggestion I will recap the amp, but trying to restuff the original paper-and-wax (when possible).
Is it possible to replace only the worn-out caps and leave the rest in for now (with proper testing) or should I just replace all of them? In other words, could you please point me in the direction where I should start first?
Thank you again all for advice, I really appreciate it!

[Enzo]

Sure, test each part. It is from experience I say the wax caps will be bad, not a just-replace-them-all. The wax is not a perfect seal, and the paper dielectric is not as robust as film.

[The Dude]

I'll add: For safety, the death cap should be removed and a grounded power cord should be added.