Amp / Pedal Guts/Mod Thread

Hemisaurus · January 23, 2011, 05:02:20 PM

My 50's Alamo Paragon, which I'm just waiting for Weber to send me the parts for a recap. NB all the current caps were made in Illinois, the electrolytics are from Illinois Co. and the polyesters are from Sangamo, made right here in Springfield, IL.

Discö Rice · January 23, 2011, 05:23:11 PM

UP IN 'EM GUTS!!

VOLVO))) · January 23, 2011, 06:37:41 PM

I love those rats nests... I'll take some pics of my random-non-working no-namer in a few minutes.

Hemisaurus · January 23, 2011, 06:43:11 PM

A Laney AOR, that passed across my bench a while back, ended up in the hands of someone on the old forum.

VOLVO))) · January 23, 2011, 06:44:52 PM

Are we in agreement that the boosts on that amp are totally useless? Also, I messaged Sleestak about making one of us a mod so we can sticky the important shit... like this!

VOLVO))) · January 23, 2011, 07:02:11 PM

This is my non-working 10 dollar tube amp. Probably sounds pretty sweet...

Hemisaurus · January 23, 2011, 07:06:31 PM

Yeah you got to bring that one by and we'll get it working, or ship it. I want to hear it too.

VOLVO))) · January 23, 2011, 07:18:48 PM

It actually does turn on, and make noise, there's just no guitar signal going through. It's not a cold joint, I already hit 'em all. It's probably in dire need of caps...

Hemisaurus · January 23, 2011, 07:21:37 PM

Marshall AVT 50, unfortunately I don't have a pic of the Pentawatt *actually 21 or so pin* single IC power amp that makes up the 50W heart of this unit, you can see the heatsink for it, in the third pic, in the middle of the chassis, with all those blue wires running to it. Hey yes, that is a real tube in the middle of the board

Hemisaurus · January 23, 2011, 07:25:15 PM

Quote from: SunnO))) on January 23, 2011, 07:18:48 PM
It actually does turn on, and make noise, there's just no guitar signal going through. It's not a cold joint, I already hit 'em all. It's probably in dire need of caps...

Have you gone through the Jack Darr Book troubleshooting procedures? I'll bet you if you follow them, basically check the tubes, the B+ voltage, and work through plate and grid from output to input listening for clicks (he explains it way better) you'll suss it out. I keep a print copy of it in the bathroom it's great.

Also what tubes are in it, and how many transformers does it have? Safety check

Looks like it might be a live chassis type, see the Darr book for more info.

VOLVO))) · January 23, 2011, 07:44:24 PM

It's got strange tubes in it... 35W4, a totally blank one, same size, so I'm assuming the same tube, a 12AU6, and another blank tube. They are Japanese, so I'm sure they aren't original. It's got one tranny, and a two prong. The tranny looks haggard, and ragged out. It works though, I always heard these things are fuckin' death traps without a ground. Since it doesn't have an OT, I can't ground it out like I would when I put a normal three prong on, right? I'm gonna have to poke through the amp, and see if I can locate it's malfunction. So far, my electronics career has been learning terms, and fixing pedals... Amps are the next step up. Draining the caps on it will be funky, I'll just have to do each lead, I guess.

also, no fuse. Death-trap.

Where can I snag a copy of that book? What's it's title?

Hemisaurus · January 23, 2011, 07:57:30 PM

Have you followed the link in my signature? Lots of info there too. That book is circa 1973 and long out of print, you can make your own copy at Kinkos, the missing section, Section III, was just a whole collection of amp schematics.

35W4, hate to tell you, you got a real suicide box there. It's not that it has no OT, it has no PT, there is no power transformer in that things, the tubes first numbers will add up to close to 110, they wire the tube heaters in series and connect them straight to the mains, usually with a ballast resistor to drop the extra voltage. I saw one once with something like a 50AX7, which is a 12AX7 with a 50V heater instead of a 12.

You'll need to figure out the weirdo tubes, the 35W4 will be a rectifier the 12AU6 is a preamp tube, are the other two tubes identical or different from each other? Can you get close-up pics?

I'd expect at least one more weirdo tube like a 50AX7 and say for argument sake there's a 6V6 in there as well.

35+12+50+6=103V

so there will be a resitor in series with the remaining tube to drop the extra 7-12V, which may have burned out since the mains voltage is usually 120V not 115V nowadays.

If the tubes are glowing, you are in better shape, it means at least the heater supply is going, NB you cannot take a tube out of this and expect it to run, like you might with a regular amp, say take out the power tubes to check the preamp section. The tubes are all part of the same circuit.

I have known people to replace the weirdo tubes with regular tubes and put a whopping great ballast resistor in there to cope with dropping 50-60V @ whatever the total current draw of the tube heaters is. There may also be some kind of voltage doubler circuit in there to step up the voltage for the plates.

Basically, this is not a fun amp to work on, one side of the chassis will be connected straight to the mains supply, so one way round of the power plug, the chassis is neutral, you can guess what you get when you flip it around. Please be uber-cautious when working on this beastie, or even just plugging into it.

tomz. · January 23, 2011, 09:13:17 PM

gut shot from my currently down Peavey Classic. have to bring it to a tech this week as I'm a electronics dufus... Sorry about the crappy pic.

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tomz. · January 23, 2011, 09:17:08 PM

this is the fuse holder that I originally put in, got bumped then shorted out and now it's vary broken...

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Hemisaurus · January 23, 2011, 09:22:07 PM

OK, done a bit of googling for you. Seems like a common setup for small amps was a 35W4, 12AU6 and 50C5.

The 35W4 is the rectifier tube, the 12AU6 is the preamp tube, and the 50C5 is the power tube. Never really encountered a pentode as a preamp tube before, kind of cool.

Now you have 4 tubes, and the front panel mentions tremolo. Here's a basic circuit that adds a 12AV6, which looks like a triode (or maybe a double, check a datasheet) for tremolo.

I'm willing to bet that your amp is going to be pretty damn similar to this. You can also check the Alamo Fiesta amp on Schematic Heaven, it has a similar setup.

Now, please, please, please read the following on adding an isolation transformer to your amp. I thought I was going to have to type a huge explanation, but thankfully someone else already has http://www.instructables.com/id/Isolation-transformer-upgrade-for-old-guitar-amps/

Hemisaurus · January 23, 2011, 09:24:34 PM

Quote from: tomz. on January 23, 2011, 09:17:08 PM
this is the fuse holder that I originally put in, got bumped then shorted out and now it's vary broken...

Nothing like shutting the stable door after the horse has bolted, but yeah, you might want to slide a bit of insulative heatshrink sleeving over the end of that fuseholder Tom, so it doesn't hit of the chassis and short again

tomz. · January 23, 2011, 10:04:46 PM

Ha! So true! Sound advice indeed Hemi, lesson learned...

VOLVO))) · January 23, 2011, 11:48:00 PM

That's one of the reasons I never bothered with it. It looks like a serious hazard. I'm probably just going to stick it in the corner again. It was ten bucks, it makes a neat decoration, at any rate. I'll consider it a lamp, at this point. I might even make it into one, for shits and giggles. I'll open my Sonaro up tomorrow, and take some gutshots of that masterpiece. Until then, a super rare amp, that only Aerosmith fans know about! Paid 250, cleaned it up, overhauled some of the bullshit fit and finish, and sold it for 450, the next day to a good buddy.

Hemisaurus · January 24, 2011, 12:06:06 AM

If you read the instructable an isolation transformer is only $12.

Or you could retube it with a flea power supply and 6V tubes, though that would cost a bit more.

VOLVO))) · January 24, 2011, 10:57:23 AM

On a lighter note, I shouldn't have sold that Bedrock. Granted, it did run 4 EL84's at 50 watts by RUINING the tubes every six months, but it was a good sounding amp...

El Zombre · January 25, 2011, 09:24:37 AM

Took some shot of my current project while down in the basement taking pictures of the Red Bear. (Yeah, I have a thing of crypto-Soviet technology)

Damn thing is visibly arcing once the electrolytics get charged up. Waiting on a 4 220uf capacitors to come in to replace them:

VOLVO))) · January 25, 2011, 10:54:08 AM

Gotta love the Russian amplification. Anyone have a MIG100/60/50? We need gutshots of those.

justinhedrick · January 25, 2011, 11:25:53 AM

i have a mig 50h, i'll see if i can get pics of it on the next few days. and sorry for the abortion of the repost of hemisaurus's pic.

hemi - you in springfield? you have a band?

Hemisaurus · January 25, 2011, 11:44:02 AM

Quote from: justinhedrick on January 25, 2011, 11:25:53 AM
i have a mig 50h, i'll see if i can get pics of it on the next few days. and sorry for the abortion of the repost of hemisaurus's pic.

hemi - you in springfield? you have a band?

You could always click the 'Modify' link, and remove the IMG tags.

Yes, I was aware you were in Champaign, Springfield is nearby, though I'm not even in the same county. Yes Hemisaurus currently still lives and is off-hiatus, we recently became a three piece again in late December, and are working on new material and a bunch of seriously reworked old material.

VOLVO))) · January 25, 2011, 08:27:18 PM

Quote from: justinhedrick on January 25, 2011, 11:25:53 AM
i have a mig 50h, i'll see if i can get pics of it on the next few days. and sorry for the abortion of the repost of hemisaurus's pic.

hemi - you in springfield? you have a band?

I will give you a cookie.

Also, this thread is important, stickied.