help with a home built amp

[JCleghorn1]

Hi everyone, I'm new here and hoping someone can help me.

My friend's father recently passed away, leaving behind a homebuilt amp that looks almost complete (to my inexperienced eye, it seems like it's missing 5 of the 8 tubes). To help carry the memory of his father, he turned to me to help him get the thing functioning again. The problem is... I'm a player with great interest in building amps, but haven't actually made the dive in yet. Can someone help me figure out what this amp needs to rock again?

I have no schematic, but can provide highly detailed pictures for anyone willing to help with this challenge. The guy who built this was an electrician and an audiophile, so I'm hoping he wasn't clueless when he undertook this project. The local music shops won't even look at it because it's home built. If it matters, you'll be helping a military member bring back a small part of what his father meant to him.

Thanks for your help

Jeff

[Firestorm]

So post 'em up. Everybody here will want to help. And Jeff, if you're military, then God bless you and thank you and all that. I didn't mean that sound so casual. I really mean it.

[Firestorm]

Oh. Give us your location.

[Structo]

Welcome to the forum Jeff.

If you want some good technical reading, check out the Reading Material on Steroids in the Technical section.

And, yes post pictures.

Do you know when he built this amp?

[JCleghorn1]

Here is a link to the pics I have so far. If more detail is needed I'd be happy to break the camera out again.

http://s816.photobucket.com/user/jeffcl ... t=3&page=1

We don't know when the amp was built or even what it was modeled after. The existing tubes are 12AX7.

I'm currently stationed in Shreveport, LA. Thanks for all the eager support and enthusiasm. I would be completely lost without it!!

Warm regards

Jeff

[Firestorm]

Pics are a bit low-res. Maybe borrow something to shoot cleaner?

Shreveport: lots of DOD there, but if it's your station, I'm guessing Air Force. Barksdale?

[RB]

Turret board looks like a Hoffman board. All those 9 pin tube sockets suggests an AC30 style build. I think the 12AX7s are plugged into output sockets. Need to see how the group of four tubes are wired(should be output section if my assumptions are correct). I am not particularly impressed with where/how the transformers are located(very long leads and OT near preamp).

Could be fun getting it running.

Welcome and Regards
Randy

[tubeswell]

50R Rk, and 4 empty novel sockets? I'm guessing either some kind of 4 x EL84 project (TW, or Matchless DC30, or stripped down AC30ish thing).

[M Fowler]

I see it now the 4th power tube is over by the preamp tubes. Either had wrong punched chassis or made an error punching this chassis reversed layout.

Hoffman AC30 looks like what he was using this amp has 30w OT and PT and choke marked 30 as well.

[ampgeek]

Fun!
Could you post up a few pics of the front face panel and/or list out the titles of the control knobs?
Cheers,
Dave O.

[RB]

I see it now the 4th power tube is over by the preamp tubes. Either had wrong punched chassis or made an error punching this chassis reversed layout.

Good call Mark. As soon as I read your comment it all clicked into place

Regards
Randy

[M Fowler]

I see it now the 4th power tube is over by the preamp tubes. Either had wrong punched chassis or made an error punching this chassis reversed layout.

Good call Mark. As soon as I read your comment it all clicked into place

Regards
Randy

Randy now the fun stuff begins plugging in tubes, making a bulb limiter, and firing this amp up. http://ampgarage.com/forum/viewtopic.php?t=20341

Mark

[drew]

Jeff, FYI the term "Hoffman layout" in the previous posts refers to an alternative style of circuit board design for several kinds of popular amps developed by a guy named Doug Hoffman. His website is hoffmanamps.com. There's a very active Hoffman Amps forum at http://www.el34world.com/Forum/index.php. Your friend's dad might have been a member over there. You might want to put a post up there to see if anyone recognizes the amp.

[10thTx]

Jeff,

I'm one of the moderators on the Hoffman forum. Several of us hang out on TAG also.

Platefire who is on the Hoffman forum lives about an hr or so from Barksdale. He may be able to help you IF you need help.

My dad was stationed at Barksdale from '67-'69 and retired Lt. Col. (Strategic Air Command) in '69. I graduated high school at Bossier High School that same yr.

Post here on the "Tweaks" section:
http://www.el34world.com/Forum/index.php?board=13.0

I'd encourage you to post over on the Hoffman forum also. There is a chance someone may know the history behind this amp.

To help you follow the layout, I am attaching a schematic that I drew up 7 yrs ago to go with Doug's (Doug Hoffman) layout.

with respect, 10thtx

[labb]

Hey 10thtx, take a look at the screen resistors on your schematic...Believe they should be 100 ohms, not 100k.