What fun can be had with this amp..?

[Lynxtrap]

I'm using the combo frame as a speaker cab at the moment. The poor amp lies on the floor in it's chassi and looks sad 'cause noone's using it.
It is an Epiphone Blues Custom 30, designed by Gibson, pcb card layout by Soldano, built in China.
The amp is quite usable. Tube rectifier. Clean channel is ok, drive channel has a funny extra mid pot that has much impact on the sound. Tonestack switchble between independent and intedependent. It doen't really sound Voxy, Fendery or Marshally, it has it's own sound. But no big personality, I'd say. With a D-styel OTS there's not much for the poor Epi to do.
It's cathode biased, and has a halfpower mode, that some genius thought they'd call "Class A". In halfpower there is an annoying level of hum introduced.
The stock reverb is useless, it has decay lasting from breakfast to noon.

Inside the chssis it looks like a chinese toystore to my eyes.
But all in all, some very nice usable functions. So if I don't sell it, what should I do with it? Strip it and make it a JTM45 Deluxe? Kick it in the butt with some KT66?
What would you do?

http://www.ppwatt.com/files/ppwatt/EPIP ... 1_DPPT.pdf

There are soundclips all over YT.

[Phil_S]

Plenty of beef in the PT. No problem doing the JTM45 with whatever power tube pleases you EL34, KT66, other choices, too. You might be able to do a lower power amp with 6V6. It has 6.3A@5A and 350-0-350 is very nice, too.

Multi-tap OT looks nice, too, but is that the tonal bottleneck?

The amp already has 5 noval sockets. You can voice one preamp circuit like the JTM45 and another like whatever else you care to choose.

Strip it! What are you waiting for?

[gary sanders]

Id love to have one of those to make a 6V6 PP with.Thats a pretty nice looking cab on those.

[Lynxtrap]

Strip it! What are you waiting for?

Maybe I should. I've planned to buy speakers for the OTS and sell the Epi. But it's really a cool amp, the cab, speakers, tonestack ideas, even the look... If it was PTP there would be no question. On the other hand, if one is to build an amp, this would be perfect since much of the job is done.
You almost got me convinced

Much of my knowledge is based on Fender amps. Would you say this amp is similar to any other particular designs? Like, loosely based on...?

[Lynxtrap]

I've been thinking about it, but I can't really decide what I want to do at the moment. I'd like to keep the odd things such as the mid control.

By the way, would it be safe to put in a pair of KT66 in this amp without any modifications at all? I have a couple of brand new (reissue) Gold Lions lying around.
Just to test something new before any invasive changes.
It is cathode biased, but can it handle KT66 safely?

[Phil_S]

KT66 and 5881 are the same pin out. The normal concern is filament current. In this case 5881 needs .9A per tube and KT66 needs 1.27A per tube. That's an increase of .74A. So, figure it out...

There are 5x 12A?7 tubes @ 0.3A each + 2x 5881 @ .9A each = 3.3A. With KT66, you'll use almost 4.1A. It says right on the schematic the 6.3V filament supply is 5A.

Is it safe to do? Now you know how to answer for that.

You may need to change the cathode bias resistor. The schematic says it's 250 ohms. I'm not sure if that will be right or not. You'll have to take readings and calculate to see if it is OK.

[Lynxtrap]

KT66 and 5881 are the same pin out. The normal concern is filament current. In this case 5881 needs .9A per tube and KT66 needs 1.27A per tube. That's an increase of .74A. So, figure it out...

There are 5x 12A?7 tubes @ 0.3A each + 2x 5881 @ .9A each = 3.3A. With KT66, you'll use almost 4.1A. It says right on the schematic the 6.3V filament supply is 5A.

Is it safe to do? Now you know how to answer for that.

You may need to change the cathode bias resistor. The schematic says it's 250 ohms. I'm not sure if that will be right or not. You'll have to take readings and calculate to see if it is OK.

Thanks for the answer! I needed the lesson, power supply is a black hole in my knowledge...

[wicker]

Hold on, first, you might try to mod what you have, change some values on pcb etc.

[Structo]

From the looks of the schematic, it doesn' look like too bad of an amp.
You may be able to tweak some values to make it suit you better.

[Lynxtrap]

From the looks of the schematic, it doesn' look like too bad of an amp.
You may be able to tweak some values to make it suit you better.

No, it's not bad. I just don't have much use for it as it is, and I find it hard to tweak anything with the PCB and tiny components. I don't have any experience with that sort of thing.
Like I said, if I do anything, I'll keep some of the nice features. Cathode bias, mid contour, half power, two channels, etc.
This could have been a nice "boutiqe"-amp if it was built for $1000 more

[Luthierwnc]

Run a pentode preamp into the bottom half of the inverter. Clubman or DC30 style -- depending on the phase. sh

[Lynxtrap]

I tried KT66's in the amp this weekend. They sort of kicked life into it, and the hum in halfpower mode disappeared. I guess the amp needs matched tubes such as these, without additional filtering.
The od-sound now has very fast and sharp attack, extremely trebly, especially in full power mode. More "Plexi"-like to my ears, whatever it means to somebody else. The mid has always been kind of "boxy" sounding, and that did not go away with the new tubes.
The clean sound is still lifeless and flat. The reverb became more usable with an AT7 in driver position.

I'm now more convinced that I don't really like this amp

[Lynxtrap]

Maybe I should start a new thread about this, but anyway....
I'm looking for some mods to try here, not too intrusive so it could be changed back to stock.

Like I wrote above, there is a sharp and fast attack to the OD (sort of the opposite of what I'd associate with cathode bias and tube rectification).
And the sound is very trebly.
The mids have a "boxy" character, for lack of a better word. I would have suspected the speakers there, but it's the same through other cabs.

How do I smooth it out? Put all that treble content to better use in more desirable frequencies maybe?

I've looked at some of the caps, cathode bypass etc. But I'm not sure where I should start.

Ideas, anyone?

[sabredude]

I have done a ton of VJ rebuilds and I basically started by re-drawing the amps in a point to point layout and replaced all of the components with better quality components just re-using the transformers. THe next step was to tweak it with different biasing and cap values and finally trying different circuits and tubes.
End result, after half a dozen Valve Juniors, I have one that sounds like a JCM 800, another that's getting close to the AFD (althought a little too noisy) and some others that sound good for blues. I don't like the PCboard epiphones but they do work great as learning tools as I have learned a ton. A the end of my last project, I realized that the only remaining component of the original amp was the power transformer so it's not going to be a big money savings tool. You might actually be better off selling it and building your next amp from scratch.

I'm seeing a decent power transformer, reverb transformer, I'm guessing a reverb tank exists, and possibly a decent output transformer. I'd lose the switching or at least be very careful about how you rebuild those pieces to keep from injecting a bunch of noise.

Listen to the other posts and make sure you don't over task that power transformer.

If you just don't want to deal with the mods, let us know what you want for the chassis and maybe one of us will take it off your hands.

You may want to consult the rules page to make sure this is acceptable but I think it is.

[Lynxtrap]

Listen to the other posts and make sure you don't over task that power transformer.

If you just don't want to deal with the mods, let us know what you want for the chassis and maybe one of us will take it off your hands.

Using the chassis and transformer to build a new amp is considered and talked about earlier in the thread.

Right now I was thinking that there could be some smaller mods to try before deciding on anything like stripping it. Like, the odd cap to cut or value to tweak here and there. That sort of thing. Like wicker said in an earlier post.

I'd have been prepare to do more involved mods if this wasn't a printed circuit board. But I thought maybe a little nip or tuck would not hurt

By the way, the BC30 is a whole other deal than a VJr.

The schematics are in the first post if anyone wants to have look, and maybe recommend something.