V-M 722 Reel Recorder Conversion - Requests for recommendations

[Zipslack]

I recently picked up a 1961-62 Voice of Music Model 722 reel-to-reel recorder for $10 US. After a visual inspection and cleaning, it powered-up and works fine. The main amp circuit is a SE 2x12ax7 with 6L6output. Plug a guitar into the Left Input and it rocks. I've attached a scan of the schematic sheet from inside the amp along with a revised version that I re-drew showing just the important stuff. Right now, all I've done is pull the 12ax7, 12au7, and Magic-Eye tubes from the non-essential circuits along with pulling the motor/fan assembly and hard-wiring the Tape-Sensor switch closed. (BTW - the 2 extra 12ax7's are British-made Mullards while the 12au7's are Mullard re-branded USA-made ;-). I'm pretty pleased with the amp as it is, but I want to remove the extra circuitry and maybe do a few mods. For starters, I need to look at adding dropping resistors to the secondaries to get the heater, rectifier, and HT voltages where they should be with modern wall voltages and am planning on a 3-wire power cord with seperate fuses for the 6.3v and 5v secondaries. The main thing I'm worried about are the odd caps and resistors sprinkled around the main amp circuit that I don't completely understand the purpose of. For starters, looking at my re-drawn circuit, what purpose does R8 serve and why is R7 there? Do either one of them need to be pulled, or left as-is? The next major area is the R/C networks on the output of the 6L6 tube. What in the world is going on there? Should I rip some, all, or none? I want to simplify things to make it easier to work on in the future. My education and experience as a technician didn't include tubes and I'm slowly trying to get a handle on things, but this circuit has a lot of things going on that I don't want to bother with, but I don't want to mess things up and have to re-work stuff.

Anyways, I'd appreciate any ideas, suggestions, and comments. I could just leave it as-is (it sounds nice and really rips when the volume is 50% or better), but I feel the urge to tinker and maybe put some of the extra input/output jacks to use.

[olddawg]

You got a lot of great parts for next to nothing. I woud buy a chassis, build up a new turret board, new pots, switches, jacks, and new ceramic tube sockets and build a new amp based on your transformers and vintage tubes using an existing guitar amp design and layout. The PT might also be able to support a PP output with an OT change for more power than the single ended design if you want. IMHE it's always better to build a new amp using those expensive transformers and such rather than trying to convert some squirrely circuit designed for something else entirely if you really plan on using/gigging with it.

[Zipslack]

Actually, I don't want to completely gut and re-build. Since I only have $10 in it, I want to try to keep the cost as minimal as possible to see what I can achieve for the money invested. Also, the unit itself also looks sort of cool/funky/retro and the built-in speakers actually sound decent. Maybe in the future I'll consider a complete rebuild... either way, I'm saving the extra pieces and parts for future projects.

[Zipslack]

Where are all the tube gurus?

Are they all gone on vacation? Consider this a mild *bump*

[zephedone]

I'm no guru or even a technician by any means ....
I have two 710 models that I found for under $10.00 . They don't look exactly like yours but very similar .The first one I gutted and put a 12" speaker and a modified Magnavox 196 console chassis in the empty cab . It runs two el84s a 5y3 and two 12ax7s . I used the PT for a PP 6v6 amp that I built into an old Peavey SS amp that was donated to me . That PT is putting out 360-0-360 vac .The second I just aquired . Am thinking about using the Xfrmrs for a SE Champ style amp with tremolo in a head configuration . I don't know what speaker is in yours but mine had a 6x9 and a small tweeter . I'm broke so , if you are like me , on a low budget , with a little work you can use everything in that old hulk but , I would transfer it to a new chassis at least as "olddawg" suggested . I have pics of what I did to mine if you want to see them . It aint real pretty but the second one I have will be much improved from what I've learned on the first build . Good luck .......

[olddawg]

I'm no guru or even a technician by any means ....
I have two 710 models that I found for under $10.00 . They don't look exactly like yours but very similar .The first one I gutted and put a 12" speaker and a modified Magnavox 196 console chassis in the empty cab . It runs two el84s a 5y3 and two 12ax7s . I used the PT for a PP 6v6 amp that I built into an old Peavey SS amp that was donated to me . That PT is putting out 360-0-360 vac .The second I just aquired . Am thinking about using the Xfrmrs for a SE Champ style amp with tremolo in a head configuration . I don't know what speaker is in yours but mine had a 6x9 and a small tweeter . I'm broke so , if you are like me , on a low budget , with a little work you can use everything in that old hulk but , I would transfer it to a new chassis at least as "olddawg" suggested . I have pics of what I did to mine if you want to see them . It aint real pretty but the second one I have will be much improved from what I've learned on the first build . Good luck .......

There seems to be a lot of dead SS combo amps around in most places that you can get for nothing or next to nothing. I prefer to start over with an aluminum chassis that will fit in the box, but if you have tools, time, skill, patience, and imagination you can usually rework an SS chassis in a dead combo and use all of those vintage parts from your doner amp on it. At least get new ceramic tube sockets and a turret/eyelet board. They're cheap and will save you a major headache.

[zephedone]

Pics ....

The last two pics are of the old Peavey Pacer amp that I used the VOM PT in . Lots of room in that chassis . I agree olddawg , it's so much easier to buy those parts and start new . Those are the inexpensive parts as well .

[Zipslack]

Thanks for the pics and suggestions

Nice work on that amp. I will probably gut and rebuild this eventually as a combo unit. This thing has a massive PT and a pretty decent size OT. And all the Mullard 12ax7 and 12au7 were just a really nice bonus I'm thinking of using the spare tubes for a firefly and/or maybe a "Rock Block" type amp in the future.

Mine does have the 6x9 and tweeter - I disconnected the tweeter to make it less trebly and because I didn't like the fact that the speakers were paralleled for 4 Ohms, but the output speaker connection is labeled for 8 Ohms. The 6x9 actually still sounds decent and will handle the power - I haven't yet hooked up to an external speaker. I still have a couple of late-60's Wharfdale's that have a 12-inch celestion in each that I will probably use (one for the combo and the other for a spare cabinet to go along with a Bogen J15).