Re: Epiphone Valve Junior

Phil S wrote:
"Jim Anable" <jim@xxxxxxxxxxxxxxxxxxxx> wrote in message news:11pgq21ta9s49a2@xxxxxxxxxxxxxxxxxxxxx

Phil S wrote:


"Phil S" <psymonds_no_spam@xxxxxxxxxxx> wrote in message news:XZKdnRz9ZqV8CgrenZ2dnUVZ_sOdnZ2d@xxxxxxxxxxxxxx


"Steve L" <surfer@xxxxxxxxxxxx> wrote in message news:ia-dnUSrm9l9eAvenZ2dnUVZ_sWdnZ2d@xxxxxxxxxxxxxx


I have seen lots of talk about this amp, and some schematics, and have decided I might try building one. It has so few parts, it can't cost very much, and perhaps if I follow better grounding techniques than Epiphone did, the hum won't be so bad.

The schematics I have seen so far don't give any specs for the trannies. I'll probably use a Hammond universal output trannie, like a 125CSE. But without any voltage specs, I am not sure which power trannie I should select.

If you can, please provide some info and advice on the trannies to use to build this little guy.

Thanks,
Steve

This amp is so simple, you could use just about any tranny in the right range and it would work. Look here:
http://www.oldradioparts.com/2a23efl.txt
This guy will sell you a 210-0-210 with 1.6A filament supply for under $10. It's perfect. #1326-054. There are a couple of other good candidates at around 200-250v per side there, too. [1] Then to get up to his $20 minimum, you go here:
http://www.oldradioparts.com/2a23dfl.txt
Get the Stancor A-3825, unversal single plate, 8W for $8.00, # *4573-102, or scroll thru and find a SP (single plate; single ended) that is rated for plate R between about 4K and 6K and whatever ohm speaker you want to drive. Make sure it is rated enough above the expected 5W output so that it can take a little abuse. You could splurge for the Stancor A-3830, NOS for $20, but it might be too beefy. There is a Stancor A-3823, an 8W model for about $7 -- I've got one in service on a Champ and I can share the "Instruction ***" with you so you don't have to reverse engineer the hook-up, as there are six terminals on the secondary. (I like Stancor.)

This is likely to be great and inexpensive iron. There is a bit of a roll the dice factor here, but at those prices, IMO, it's very low risk and has a big upside in terms of both cost and performance. With the price of iron under control, you can actually beat the street price on that amp and have a better product. You can buy terminal strips at Rat Shack -- you don't need a fancy eyelet or turret board for this one.

Go for it!

Phil

[1] You need 1.06A for the filament supply for a 12AX7 and a EL84; get a little more to be safe. The rough rule is secondary AC (n) through the diode bridge = n*1.4*.85; in this case, ~250vdc to the plates, give or take. EL84 is good with plate voltage between about 250 and low 300's. I've got an amp that runs them at 315v.



I forgot to mention, that I like Weber for inexpensive parts (caps, resistors, switches, sockets, wire, etc.) and you can probably get everything you need; maybe even a chassis, too. With the cheap iron and small parts, you're probably looking at about $60, including shipping. That doesn't include the chassis, tubes, speaker, or cabinet. To do this as a combo, I'd expect to be a bit north of $200.

It might be cheaper to actually buy one, gut, and rebuild it! You get to keep the cab, speaker, tubes, chassis, and iron. Maybe even salvage some of the other parts.

Yep! I agree. I posted on your first message before reading this one.


As you can see by the posting times, this one gnawed at me for a while. I think that's because I'm the guy who likes to do it the least expensive way possible. <Go ahead, call me cheap!>

There is NOTHING wrong with being economical. You can end up with MORE GEAR that way!

When I finally got to this conclusion, I thought, if I didn't already have that FrankenChamp head I built with the 6AQ5 and 12AT7, that I would do this very thing!

Now, I've got to thinking that I could build one with that spare PT I've got in the basement. I think it's 250-0-250 and only has a 6.3v filament winding. I was hoping maybe it would be OK for an 18-watter, but I'm not sure the filament winding has enough amps in it. I'd still need the "small parts" and a chassis. The trick is finding a cheap and good quality donor chassis on eBay.

That's how I did my Matchless Spitfire circuit (I don't call it a clone, because I used existing iron). I picked an old hi-fi amp with the right tube compliment, and went from there.

I've got an OT and sockets; and enough wire for a Valve Jr.

Anyhow, I'm too busy right now; working every day, all day, telling clients they have to wait. It isn't always like that. I'm self employed and I'd like to keep it that way for a while, if I can.

Phil 


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