Kelley Clone

[Runaway J]

Hi!
I’d like to convert my old Fender 75 into a Jim Kelley FACS amp.
A guy I knew in the 80’ was the distributor of Kelley amps in Germany and they were really amazing amps.
At that time a strong competitor of the dumble amps.
First I planned to make a dumble-clone out of the Fender, but I already have one on the workbench and 2 more planned,
so – how much dumble clones does one need ?
The Fender has exactly the right faceplate-layout but runs on too high plate voltage for 6V6s, so I’ll try it with 6L6s.
I got the schematics and some pics from the internet, but can’t find a schematic for the original attenuator.
Can anyone help ? Has anyone ever built a JK FACS clone or has experience with the original amp ?
Thanx!

[David Root]

"The Fender has exactly the right faceplate-layout but runs on too high plate voltage for 6V6s, so I’ll try it with 6L6s. "

The FACS amp runs 485V plates on 6V6s, and 460 on the screens. The Fender 75 shows 500V plate, and presumably about the same on the screens, which might be pushing it a little in a FACS circuit. NOS 6V6s are tough little buggers, and there are even some tough current production ones too. JJ & "Tungsol Russian" spring to mind. 6V6s were designed for 15% duty at 1200V, so they can sure handle 500V plate on 100% duty in the right circuit. I might be a little uneasy about the screens, but it's probably worth a try. Might be a bit different tone too with the UL OT.

[/quote]

[drz400]

I've owned 4 Kelleys myself
Great sounding little amp
Most unreliable amps I've ever owned, They eat 6V6's for breakfast.
This was like 25 years ago but those amps shut me down many times.
They run too hot. I dont care what they "say" a 6V6 should be able to handle ... they never lasted for me in that amp. I would run lower voltages than Kelley did. I had to put 5881's in mine to keep them working.

[mlp-mx6]

Perhaps "non-spec" screen resistors would help. What is the specified screen resistor? I'd suggest AT LEAST 1K cement.

[David Root]

On the schematic I have it is a single paralled 2k 10W, fed from the plate B+ node.

[mlp-mx6]

I looked at that schem on Schematic Heaven also. Never seen a shared screen resistor before.

According to O'Connor, too much screen current is what kills most power tubes, when they are killed quickly as was referenced earlier in this thread. Limiting screen current via larger screen resistors (uh, and maybe individual resistors) will thus save the tubes.

[David Root]

Shared screen resistors were not uncommon way back in the day, but I don't recall seeing them used in this late much, if at all. At 10W this should be pretty safe, BUT... if it did fail...!!!

[Runaway J]

Thanks for the replies.

Does anyone know where I can get those pots
(500k lin push/pull, solid shaft) for 'treble' and 'bass' ?

How does the amp sound with 5881's ?

[Runaway J]

BTW I just found the following story on
http://studentweb.eku.edu/justin_holton/bias.html

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What follows is a review of the JJ 6V6S by Lord Valve. I am unable to find the original source, but I found it so interesting that I decided to include it here. Judge for yourself.

"I just got finished doing the matching on my first batch of JJ 6V6s. Just for fun, I decided to see if I could kill the last tube in the batch. A good batch, BTW - only 2 croaked out of 150 during the 48-hour stabilization burn. And something odd - *all* of the 148 tubes that survived the burn fell between 13 and 21 mA during matching. I've never seen a batch of *any* power tube fall into a range that narrow. Somebody's doing something right at JJ. This is a BEEFY-looking tube - it's built in the same bottle as the JJ GZ-34, which makes it larger than any non-Cokebottle 6V6 I've seen before. The plates are also considerably larger than other 6V6s. Meaty!
Anyway...I decided to see how much current I could pull through the last tube before it red-plated. My test voltages for 6V6s are 425 plate, 425 screen, -40 G1. This particular tube read 15.6 mA at those voltages. I increased the current to 30 mA. No sweat. 40 mA. No signs of distress at 17 watts static, which is beyond ratings for this tube. 50 mA - no problemo. Still no red, not even a stripe. At 21.25 watts, we're well into 6L6 territory. (BTW, I let the tube cook for around 10 minutes at each level.) 60 mA - 25.5 watts static, passing max EL34 ratings now. No stripe. Jeeze...cue X-files music? SEVENTY mA. Beyond max spec for a 6L6GC...and *finally* a narrow red stripe on either side of the plate. I let it sit for ten minutes - whacked it with a nutdriver handle a few times. Happy as a clam. OK, I cranked the bias down as far as it would go...81.4 mA through the tube. The red stripes got wider, but nothing else changed. I let it sit ten minutes, then shut it down and let it cool off. After a half hour, I powered it back up and took readings from it at my standard test voltages. How' bout dat...15.7 mA, within 1/10th mA of the original reading. Aside from the fact that part of the logo burned off, the tube showed no signs of misuse.
I have no idea how these tubes sound yet, but I do know *one* thing: they are *damn* hard to kill. I sent two quads to Doug Roccaforte today; we'll see what he has to say about 'em. And if Jim Kelley is reading this, give me a call. *Your* amps are the most notorious 6V6 killers on the planet, and I think I may have something for ya. Interested in your take on the tone."
-Lord Valve