420 -> 5e5/5e7

[Capacitordeath]

Hi! First time poster here, and looking forwards to plenty of reading from this forum.

So, here's my story. I've been wanting a tube amp for a long while, and something that doesn't howl like a wounded pig. Granted, Deizels (sp?), 5150s, JCM2000s, and Triple Rectified hold a certain fascination to me, but I think I lost the need of that sort of tone a few years ago. I discovered the Tweed, and through vigilant studying, found that the "mild" sort of tone that I like was also one of the simpler amps to build, so to speak. Not a lot of parts, no circuit boards to acid-dip, etc.

Fast forward to today. I traded a piece of MIDI equipment that didn't work on my stupid Vista machine (don't buy Akai) for a weird old tube amp from an organ. I immediately started salivating a'la Pavlov's dog, and started opening it to look inside.

I didn't touch anything!!!!!
I've been reading enough of this stuff online to know that one of these mysterious firecrackers in there could stop my ticker. I dunno which one, exactly..

Anyway. So here's what I have, and here's what I want. A Wurlitzer 420 power amp for a Leslie-style speaker. It's got 2 nice clean 7025a power tubes, a 12au7 tube that's probably the phase inverter, and a 7199 tube that sits in front of the "stack", along with a 5u4ga rectifier tube. There's a sort of normal sized output transformer, and a gigantic power transformer (I'm assuming that because the rectifier tube is sitting right in front of it). A couple of those tall twist-on capacitors from Sprague sit on top, and a whole mess of capacitors from RMC and Good-All, Some of which range into 1400 volts.

So, I went to the Fender Field Guide, and searched until I found an amp that had the rectifier tube, and something close to 7025a (which are apparently a quiet version of the 6l6), and came up with the 5e5 and 5e7 amps. Therefore...here I go.

So, my plans! I would like to end up with a Pro/Bandmaster with an effects loop, and the ability to switch between one or the other speaker, as I would like to put in a standard magnet speaker and an AlNiCo one. I don't really want it to look like a Bandmaster or Pro as I'm sort of scratch-building it. I'm thinking a nice "woodie" combo.

Here comes the fun part. I have no clue what I'm doing with electronics. I do know that caps will kill me if they get the chance, and to never lick the battery out of your laptop (a friend demo'd this little activity). So, I DLed the schematic of the 5e5, and the chassis layout. Looks kind of like connect the dots, only with solder. I understand there's a lot of checking that goes into an undertaking like this, which includes a check of the non-tube parts before I blow anything important up.

Also, I should look for a source of the parts I need. Does anyone know if the 7025a power tube is a decent trade for a pair of 6l6gc? How about a 7199? I've read that both of these are more suited to the Hi-Fi crowd...

Anyway...there's my story. I need to learn how to desolder, and get my ducks in a row. There's about twice as many parts in this Wurlitzer organ than there are in a Bandmaster, so I'm hoping I'll get the lucky.

Thanks for letting my air my laundry!

[Capacitordeath]

Oh, here's a pic of the outside of the chassis. I'll post one of the inside soon.

[tubeswell]

Hi there and welcome to the forum and the addictive and dangerous pastime of mucking about with tube amps. Yes tube amps can be lethal. Be careful of the filter caps - they are the large caps that are capable of storing high voltages even in a powered-off state. You should ensure these are discharged (in a safe way) before working on the amp. It would pay for you to do some reading (No amount of knowledge is too much). The Jack Darr book is a good place to start.

http://www.pacificrecone.com/JackDarrBook.html

Looks like you've probably got most of the key bits you need there (assuming they are all working). The one thing I would definitely get new parts of are the electrolytic capacitors. These are the caps that are in the filter cap can, as well as the caps that are the cathode-bypass caps.

Looking at the tweed bandmaster, you're going to need:

filter caps
3 x 16uF-20uF 450V-500V and 1 x 8uF-10uF 450V

bias supply cap
8uF min. 100V-150V

cathode bypass caps
2 x 22uF-25uF 25V

You may also need to get all the coupling caps (or at least the values you haven't got already) even tho' these will usually still be alright (unless you have one or two leaky ones, which you will find out when you come to fire up the amp for the first time).

You also need to check that the trannies are in working order. (Easy to check if you have a variAC supply and a couple of multi-meters - and are careful).

And I would probably wire the AC mains connector to a 3-wire system (with the chassis grounded via the 'earth' wire) to ensure that the chassis is put at ground potential.

[Capacitordeath]

Hi. Here's some more shots of my organ amp, specifically, the innards.

I've got a shot from behind the tone knobs. I'm sort of surprised at the messiness of the electronics in this thing. Also, there are some of the pieces that have some white, flaky rot on them. I wasn't really planning on using anything in here, but I imagine this stuff needs to get round-filed out of uselessness.
You can see the 7199 socket under the haphazard pile of resistors and capacitors. The power tubes are at the bottom there...

The other shot is from the other side of the amp. There's a set of little guys that look like transformers. Would these be inductors, possibly used as a choke? The power transformer is just above the shot, and the rectifier tube socket is in the shot, yet again under a pile of stuff.

If these little dudes are this machine's choke, would they make a reasonable addition to the new guitar amp? I'm not worried about a correct look, so to speak. If these little dudes will work, I'd rather go with an oddball style. Think Trillium Seraph, only less cultured. If it's got a couple odd little nubbly bits hanging out at odd angles, all the better.

[tubeswell]

The other shot is from the other side of the amp. There's a set of little guys that look like transformers. Would these be inductors, possibly used as a choke?

Not quite sure what you're talking about. I can't see anything that looks like a choke in those pics.

[Capacitordeath]

Well, I took a close look at them, and and the other similar device that you can see the edge of at the bottom of the pic on the right.

I think they're relays. The one of the bottom is definitely a relay, and the three little ones at the top are as well.

What can be done with these besides making them go away?