Epiphone Valve Senior MOD

[CaptainHammock]

Hi everyone,

I’ve started a combo mod project and I’m posting my progress here to get your advice and keep a log of feedback on this amp.
I’m a beginner when it comes to amp electronics, so apologies in advance if I say anything completely wrong.

Goal:

A portable 15–20W tube combo, Blackface-style, with a 12" speaker.

Budget:

About $540 including mods.

Intended use:

Rock, Blues, Funk, Hard Rock. Small gigs. Strat, Tele, Les Paul.

Skills:

I’ve redone the wiring on my guitars, but that’s about as far as I’ve gone.

Shortlist of donor amps:

Fender Blues Junior – 15W – 2xEL84 – 1x12
Laney Cub12R – 15W – 2xEL84 – 1x12
Traynor YCV20 – 15W – 2xEL84 – 1x12
Ampeg Jet J-20 – 20W – 2x6V6 – 1x12
Bugera V22 – 22W – 2xEL84 – 1x12
Marshall DSL20CR – 20W – 2xEL84 – 1x12
Epiphone Valve Senior – 18W – 2x6V6 – 1x12

I decided to prioritize 6V6s to get closer to a Deluxe Reverb feel, and to wait for a good deal.
I found a near-mint Epiphone Valve Senior for $250 and went with that.
It's a forgotten amp that did not sell that much but I think it has some potential.




Pros / Cons:

Really nice cleans and edge-of-breakup tones, with a full EQ and practical gain/volume interaction.
Looks cool, not a common amp, I like it.

BUT:

Reverb is unusable past 9 o’clock (I’ve got a pedal, but still a shame).
Known to run hot, with premature tube wear and component failures.
Doesn’t really nail the Deluxe Reverb sound (no surprise), OD is a bit mushy in the lows, and the Presence control barely does anything.
No FX loop (not an issue for me), and it’s heavy (I’m on foot, so not ideal).

Mods planned:

I’m focusing on changes that improve tone and reliability, while keeping the budget in line with the amp.

Speaker upgrade ($85)

Stock Eminence Lady Luck is decent but breaks up early, not very Jensen-like.
Swapping for a WGS G12C (70W, 8Ω) to increase headroom, tighten bass, and get closer to the Jensen sound.
Optional but impactful.

Transport mod ($11)

Picked up an old frame pack ($10). I’ll strip the canvas and strap the amp + pedalboard to the frame for easier carrying.
Thought about adding a tilt option, but won’t leave the frame on stage.


Tone stack mod ($11)

Stock circuit is Fender/Marshall-ish with different values.
I want to get closer to the AB763 (Deluxe Reverb / Princeton Reverb) but keep a Mid control.
Stock TS:
R5 56kohm (1/2W)
Treble cap → C7(C6) 150pF, pot → B1M
Mid cap → C1/C2 22nF/400V, pot → B25k
Bass cap → C3/C4 22nF/400V, pot → A1M


Modded TS:
R5 → 100k(1/2W)
Treble cap → 250pF, pot → A250k
Mid cap → 47nF/450V, pot stays B25k
Bass cap → 100nF/450V, pot → A250k


Bias correction ($5)

Reports say the stock 6V6s run super hot (like 140% from my rough calculations). One user even blew the cathode bypass cap.
Replace C25 → from 22µF/50V to 33µF/100V (better reliability + thicker bass).
Replace Cathode resistor → stock 250Ω replaced with 390Ω (bias~90%) or 470Ω (bias~75%) to cool things down.
I haven't measured anything yet. Will experiment and adjust. Open to advice here.



Reverb stabilization ($20)

R28: 330k → 200k
Reverb tube cathode resistor: ? → 2.2k
Tube: 12AX7 → 12AT7
Copying known fixes, will learn as I go.

Presence mod ($4)

Presence control barely affects tone. Plan to shift/expand the frequency range.
C41/C40: 1nF → 4.7nF
Pot: B25k → 50k linear

Coupling cap swap ($8)
To tighten bass and clean up OD, aiming for more “Strat bounce.”
PI → 6V6 coupling caps C17/C18/C19/C20: 100nF → 47nF



Cooling ($12)
Considering cutting the back panel to add 2x 12V fans for tube cooling. Will first test cooler bias settings to see if it still overheats.



Tube upgrade ($190, gradual)
Not really a mod since it’s consumables, but I’ll eventually run 2 x Tung-Sol 6V6GTs + 2 x EHx 12AX7s and EHx 12AT7.

Reverb tank upgrade ($32)
Accutronics 8AB2A1B. Low priority.

With shipping and extras I’m still within budget (excluding tubes and tank).
Add a few small things like alligator clip leads for draining filter caps ($3), and I’m on budget. Parts are ordered, so now it’s time to dig in.

I’d love to hear your thoughts and any advice, since I’m new to amp mods. I’ll keep updating with my progress.

[maxkracht]

Not entirely sure what you are asking but i'll take a stab.

I decided to prioritize 6V6s to get closer to a Deluxe Reverb feel

If you are shooting for deluxe reverb, you might want to change the amp to fixed bias instead of cathode biased. This would require changing the master volume and finding room for another board. Considering how much of a pain that would be, making the 6v6 cathode bypass cap arbitrarily large can get you a bit closer, say 470-1000uf to keep the cathode voltage more stable. A 50v cap is fine, thats more than double the expected voltage. The failure you reported is more likely due to a cheap cap and/or the cap being too close to a hot cathode resistor.

You might also want to change plate and cathode resistors in the preamp closer to standard fender values. 1-2w metal film for the plates can lower noise slightly.


The note about probing the phase inverter cathode doesn't make sense, but in conjunction with the reverb being unstable makes me wonder if there are some serious layout problems causing the amp to oscillate. I've never worked on one of these, so I can't point you to any specifics, but fixing this may require cutting traces on the board and adding shielded cable runs or physically moving components.