Epiphone Pacemaker Re-Cap Questions. Update! It Lives!!!

[rlh5599]

I picked up a '66 or '67 Epiphone EA50T Pacemaker in a trade the other day.  Needs the usual maintenance, caps, cord, etc.  Same circuit as the Gibson Skylark from the same period, I have a schematic, no worries there. 
The Caps aren't bulged or leaking, but I know the drill, better safe than sorry.
The filter caps are the cardboard multi-cap style, 1 is a 20-20mfd 450v, the other is a 20-20mfd 325v. 
Does anybody still make this style cap, or would I just be better off with 4 20's on a little board?
I thought about a can cap, but don't want to change the chassis, there's room for 4 20's where the 2 caps are now.
Should I change out the diodes?  I want to keep the circuit stock for now, I know these are a bit jangly, but I can "fix" that later if I want.  Right now I just want to make it work.

Kinda funny/scary story, The guy I got it from picked it up several years ago at a local second hand store and said that when he plugged it in, it had a loud hum, but you could hear "guitar" thru the hum, albeit very low volume.  The power cord is mangled, electrical tape holding a splice together, he said he got a "tingle" when he touched the strings on his guitar.  I told him I trusted him, didn't care, because I was going to do some maintenance before I plugged it in, and that he was quite lucky it wasn't his wife trying to sell it to pay Doctor's bills...

Any way, a couple shots of the amp and guts.

[sluckey]

Very clean. I'd turn it on and evaluate before just replacing stuff. Measure some voltages, etc. If the diodes check good I'd leave them. I'm surprised they used one silver and one black.

You'll probably end up replacing the caps. I would not bother with a board for individual caps. Just a terminal strip. I'd be very tempted to use that JJ 40/20/20/20 can for a neat installation.

Would you post your schematic? None of the ones I have use diodes.

[eleventeen]

I'd use individual PC (radial) mount caps, available for about $1.50 each. (Might as well go with all 450 volt ones) I would try to swing the power resistor and the black cap at the top of that strip over to the other side (the transformer side) of the terminal strip. Silicone the caps to the chassis. You can leave the current caps right where they are, there should be room for the PC mount ones in the space available. The way the leads come out of the  new caps will be perfect for how the connections arrive at the term strip. You may have to extend the leads some; try to use some heavier wire to aid in stiffness and put some insulating sleeving or heat shrink around the leads. You could use the jacket from a scrap of shielded cable, free.


I'd also replace the bias (?) cap while you're in there just on gen'l principles.

That amp does NOT appear to be the same as a Gibson "Skylark" which is a 5 watt single ended single 6BQ5/EL84 job. It is closer to but still not quite the same as the Epi GA50T in Doug's library which is a 5-tube with 6X4 tube rectifier amp. You probably don't need the exact schematic if you simply replace cap-for-cap, but assuming you would want the real schematic for future reference, you will have to dig a little bit because Gibson & Epiphone are kind of notorious for having variations like that (eg; tube recitifer in one and SS diode in the other) all over the place but with the same model numbers.




 

[rlh5599]

It actually uses two silver diodes, just hard to see in the pic.
attached is a copy of the schematic, same as the Gibson GA5-T from the same time. 
The Pacemakers and Skylarks used this circuit in 65-67 and added a trem.
This schematic matches what I have exactly.
I have a high res schematic too, if you'd like I can email to you.
 Edit, it actually is a black diode and a silver one...

[vibrolax]

The non-tremolo version of this amp was the first guitar amp I owned when I was 9 years old.  I believe my parents paid $88 for it (new).  One of the diodes failed and that was the last time the amplifier worked.  Unfortunately, my 11 year old self was better at taking things apart than understanding how to repair them and put them back together again.  So it moldered in the back of the closet for a few years then ended up on the curb. 

I've run into a few of them for sale in various musical instrument stores in the last 5 years, with asking prices around $400.

BTW, I agree with others' advice to replace the filter caps with replacements mounted to a terminal strip.  I'd definitely replace the diodes with modern silicon.

[PRR]

> he got a "tingle" when he touched the strings

And they called it a "Pacemaker"??

[shooter]

everything was bigger back then

[rlh5599]

> he got a "tingle" when he touched the strings

And they called it a "Pacemaker"??

Funny, huh??  and people argue over grounded cables and death caps..  A guy didn't know the risks, could've been hurt, or his kid...

[rlh5599]

So I have some new 6A10 Diode Rectifier 6A 6 amp 1000V Diodes.  I realize they may be a bit of overkill, but will they work as diodes for this, or should I order 4007's when I get my caps?

[sluckey]

Either diode will work just fine. 1N4007s are dirt cheap. They ain't no better than the 800V silicon top hats that are in it now. I would not change them unless they are bad. Diodes do not slowly fail, drift, become weak, change value, etc. They are either good or bad. No in betweenies.

[PRR]

Ten dollar diodes in an amp that wasn't worth ten bucks new??

I like over-kill but this is a little over-over-board.

It's your money.

Wise to invest in a 10- or 100-bag of 1N4007 diodes. They will do for about 98% of anything tube-ish, and all small chips. While a 1,000V diode in a 12V system is over-kill, at 10 cents or less apiece it isn't worth fretting over.

[kagliostro]

And they called it a "Pacemaker"??

Yes, everlasting Peace-maker 

Franco

[rlh5599]

Ten dollar diodes in an amp that wasn't worth ten bucks new??

I like over-kill but this is a little over-over-board.

It's your money.

Wise to invest in a 10- or 100-bag of 1N4007 diodes. They will do for about 98% of anything tube-ish, and all small chips. While a 1,000V diode in a 12V system is over-kill, at 10 cents or less apiece it isn't worth fretting over.

Nah, got 'em for 5 bucks for a bag of ten for another project, never used 'em, they just sit here..  When I order the other parts, I'l get a bag of 4007's, just curious as to if they'd work, figgered they would..

[rlh5599]

So, The guy I got it from was right.  Nothing in input, All controls @ Zero, Plug it in, turn it on , LOUD hum, gets louder as time passes.  A LOT louder, very quickly.  New 3 prong grounded plug, fixed a couple sloppy solder joints on the terminal strip, checked diodes, checked cathode bias resistor, and voltage at 1st cap (about 320v), before I couldn't take the noise, almost went into feedback.

Just get filter and cathode bypass caps?  R&R Tubes? 
Any thoughts appreciated, my first recap attempt but I've built a couple amps with new parts..
Thanks!

[sluckey]

Take smaller steps. Do the filter caps first. Then recheck.

[rlh5599]

Thanks Steve!!  Making an order Monday.  The shaft on the Volume pot is broken, calls for a 250k, can a 500k be subbed??

[sluckey]

You can. But since you're making an order just get the right pot. It's only a couple dollars.

[rlh5599]

Yeah, figgered, Thanks again!  Going to go ahead and order some service parts, resistors, coupling caps, etc.   Nothing is more frustrating than having to wait for parts, even if it is from Doug, the Fastest Shipper in the World..

[rlh5599]

So, I replaced the filter caps and the cathode bias cap, and cleaned up some more bad soldering on the term strip, and VOILA!!  sound.
It's dead quiet, even with the non-twisted heater wiring and basically terrible lead dress.
VERY twangy, very odd, (to me) tone controls.  And it doesn't get very loud for a 6BQ5 PP.  (no where near as loud as my Stout TMB, through the same speaker, etc)

I haven't changed any other parts, but I did find on the innerwebs the following suggestions to boost low end and gain a bit.
Any thoughts??
and a shot of the cleaned up guts.

[shooter]

it doesn't get very loud

Did you measure PA circuit volts?
I had a 5T that sounded good but low vol, half the OT was bad, anyway
fwiw

[rlh5599]

it doesn't get very loud

Did you measure PA circuit volts?
I had a 5T that sounded good but low vol, half the OT was bad, anyway
fwiw

seems like all the voltages are good, except I can't get a steady reading on pin 6 of v1, the 6EU7.  Understand I'm just a green hobbyist, still learnin' but not up on all the 'lingo'.
It sounds good, and is usable if I monkey with the tone controls, just lacks 'balls', if that makes any sense..

[Willabe]

Any thoughts??

Yes, 1st try disconnecting the T filter/mid range notch as shown in your schematic. If you still need more, maybe try these in this order, 1 at a time, leave 1 in place, then add 2, then add 3, then add 4;

1. Bypass/remove C1.

2. Change R10 to 1MA.

3. Change R3 to 1M.

4. Change C3 to .02 or .047.

[rlh5599]

Any thoughts??

Yes, 1st try disconnecting the T filter/mid range notch as shown in your schematic. If you still need more, maybe try these in this order, 1 at a time, leave 1 in place, then add 2, then add 3, then add 4;

1. Bypass/remove C1.

2. Change R10 to 1MA.

3. Change R3 to 1M.

4. Change C3 to .02 or .047.

Thanks for the tips, I'm reading and trying to figger out why things do what they do, and what changes make the differences they make.   All your help and suggestions help a ton!

[HotBluePlates]

... VERY twangy, very odd, (to me) tone controls. ...
I haven't changed any other parts, but I did find on the innerwebs the following suggestions to boost low end and gain a bit. [In the photo]

Your amp's Bass control comprises the pair of resistances in a bridged-T filter, which is marked in the pic you have as a "midrange notch".  Normally we could call a bridged-T filter a "mid notch" if the values were fixed, as that's how it's often employed in a guitar amp.

But your Bass pot appears to change the effective values of the resistors in the filter from "1MΩ & 1MΩ" (with the Bass pot at minimum) to "50kΩ & 50kΩ" (with Bass pot at maximum).  That is, it bridges a 100kΩ resistor across the Bass pot, which will probably look to the circuit the same as two 50kΩ resistors in series.  If that guess is true, sweeping the Bass pot really shifts the center-frequency of the notch from a low of ~71Hz (Bass at minimum) up to ~1.4kHz (when the Bass pot is at maximum).

Yes you could cut out the bridged-T filter circuit (or change parts values), but I suggest trying this first:
 - Set the Treble control to maximum (it's just a roll-off control anyway, so you'll be throwing away less signal).
 - Pretend the "Bass" control is labeled "Notch" then ignore the numbers and turn it until you get a good bass/treble balance with your guitar.
 - Only turn down the Treble if you have too much high end once you've dialed in a good amount of lows with the "Notch" control.

The "Notch" control is moving around a fairly deep, wide notch.  It just so happens that if you turn the control down so the notch is in the guitar's bass range, it sound like bass has been turned down.  But it doesn't behave like the slider on a graphic EQ or the Bass knob on a James-type tone circuit, which turns a given frequency band up/down.

If you absolutely can't live with it, you'll probably find more functionality replacing the Bass & Treble controls with Fender-style tone controls, perhaps with the associated caps mounted on some perfboard behind the newly-replaced pots.

I disagree with the photo's recommendation to raise the cathode bypass caps up to 20µF (but I also haven't heard/tinkered with this amp first-hand).  2µF against 1kΩ is still -3dB at ~80Hz which is roughly the Low E, so it covers the guitar's range.  5µF against 1.5kΩ extends full gain even lower.  It would be nice to know that whatever caps are in your amp haven't dried up to be much lower than stock, as that would then reduce bass.

I'd probably raise R3 to 1MΩ.

...  And it doesn't get very loud for a 6BQ5 PP.  (no where near as loud as my Stout TMB, through the same speaker, etc) ...

If you drive the input jack hard enough, it will probably be as loud as any other EL84 push-pull amp.

But the circuit overall is 1/2 of a 12AX7 into a lossy tone circuit into 1/2 of a 12AU7.  The interstage phase inversion transformer may give some signal boost (or not; would have to measure to know).  This all adds up to an amp which stays cleaner (or seems to sound weaker) than another amp with much the same output section but  more amplification in the preamp.

R8 before the Volume control also reduces signal level by at least 2/3rds.  You'd raise overall volume if you removed R8 (or replaced with a piece of wire) and used a 1MΩ audio pot instead of 250kΩ.  You could do what the picture you posted shows, but you'll be loading the input 6EU7 and somewhat reducing its available output before distortion.

[rlh5599]

Thanks for the suggestions HBP!  Any and all thoughts are appreciated.  Right now I'm gonna button it up and play with it for a while.  I'm kinda enjoying the cleaner aspects of it, just a matter of getting it all dialed in, and making sure everything is 'in spec'.

Thanks again!

[sluckey]

seems like all the voltages are good, except I can't get a steady reading on pin 6 of v1, the 6EU7.

That's normal. That triode is the tremolo oscillator. The changing plate voltage means the oscillator is working. If you turn the tremolo off with the footswitch, pin 6 will become steady.

[rlh5599]

Thanks Steve, after I said that I kinda traced things out and figgered that was probably the case.

[rlh5599]

So, I got everything serviced,  replaced the cathode bypass caps, (5uf @ c2, and 2uf @c7) with 10uf's I had layin around, new 500 pf @ c5, a 1meg @ r3, checked all the resistors, and I installed an output jack.. 
Sounded like poo, no volume, very little oomph.   
Bummed.  Walked away for a couple days
Looking at the schematic, I noticed one side of the output trans is grounded.
Sure enough, I wired the new output jack backwards.
Rewired the jack, BOOM, sounds like it should.  (Probably lucky I didn't blow something up...) it is a VERY clean amp, still not as "loud" as my Stout, but OK.
I placed a jumper across R8, and that made a BIG difference in volume, still have plenty of control with the 250K, I think I will make the jumper permanent.

It is an odd "tone" arrangement, but with a little fiddling with knobs, it gives quite a bit of range.

Once again, Thanks for all the help and advice.  I managed to keep it pretty true to original, (could have ripped everything out and made it a Pro Junior or an 18 Watt light)

Fun little amp,
Thanks Again!!