Voice of Music Amp - VM 160

[tigerzilly]

Got the new caps in and replaced one tube socket. The amp had a three prong plug, but only two conductor wire. Replaced the power cord and grounded. Amp powered up and passes good signal. Plugged a guitar into the 1/4" microphone jack. Decent sound with fair volume. The original 10" speaker has some buzzing . Got it running through a 12" and it sounds much better.

[Chuck H]

Please make these changes and let us know how it works out

[tigerzilly]

Please make these changes and let us know how it works out

I presume that change will make it more guitar friendly. Any thoughts on Jensen P10S alnico speaker? It gonna need a recone. Is the speaker worth saving?

[Chuck H]

I presume that change will make it more guitar friendly. Any thoughts on Jensen P10S alnico speaker? It gonna need a recone. Is the speaker worth saving?

Jensen's "S" model was a step below their "R" line. I have no idea what the real world difference is between the p10s and the p10r, but the p10r is the more desirable speaker. That being the case you wouldn't really be money ahead to recone it. And being as this will never be a collectible amp I wouldn't be concerned about preserving the original speaker for it either. But it's probably a perfectly good sounding speaker and if you did have it reconed it would probably get "R" parts anyway.?. I think the magnet was the same on both speakers. So in this light I'd probably look into the cost of a recone vs. say, a new Weber or something and then go with the cheaper option.

[tigerzilly]

I can get a Jensen MOD for $35. Recone is $65. I can store the original Jensen away in the unlikely event it adds value.

[HaroldBrooks]

Ok. I know I have a problem. The first step to recovery is to admit the problem. I'm a vintage tube amp addict! Here is my latest acquisition. Appears to be about 1952 Voice of Music Model 160 amp. Its not a guitar amp, but it looks like a good candidate. Here are the pics as it arrived.

[ATTACH=CONFIG]56730[/ATTACH] [ATTACH=CONFIG]56731[/ATTACH] [ATTACH=CONFIG]56732[/ATTACH]

Here's what you amp 'problem' reminds me of...


https://www.youtube.com/watch?v=URSnFwRGw_I



You came to the right place for help... if you never want to get better that is !


THAT FUTURE GUITAR AMP LOOKS GOOD TO ME !

[Chuck H]

I can get a Jensen MOD for $35. Recone is $65. I can store the original Jensen away in the unlikely event it adds value.

I've never tried the MOD, but I've read that it's designed for a very wide and flat frequency response for modeling amps that simulate different cabinet types. And that doesn't sound great to me for a basic toob amp. $65 bucks seems like a good price for what will basically be a new speaker. And if I'm right, the magnets are the same AND they recone with "r" parts you'd be getting what amounts to a new p10r for $65.

[tigerzilly]

$65 bucks seems like a good price for what will basically be a new speaker. And if I'm right, the magnets are the same AND they recone with "r" parts you'd be getting what amounts to a new p10r for $65.

The P10S appears to be a 9 watt speaker. The amp according to the schematic is 8 watts. Seems it would be nice to have a little more margin above the amps power rating. Will R parts give the speaker more power handling.

I have used the Jensen MOD in the past. No complaints at all.

I started making those changes you recommend. I need to order the 2.2uf cap. The 1M and 47k resistors are in.

[Chuck H]

The changes work in tandem, not individually. The operation of the tube is altered from grid leak to cathode bias. The 1.5k cathode resistor in place of the 4.7k will increase signal sensitivity at the input and run the tube at a higher idle current. This is when you need the 1M grid load resistor instead of the 4.7M that was in there. You could use any capacitor value over 470n for the capacitor parallel to the 1.5k cathode resistor. I think a value of 2.2u or smaller is best because there's really no high pass filtration like most guitar amps. A partial bypass on that stage will boost above a frequency dictated by it's value. Smaller = higher frequency knee. Anything over 3.3uf is basically all audible frequencies boosted.

[Chuck H]

The P10S appears to be a 9 watt speaker. The amp according to the schematic is 8 watts. Seems it would be nice to have a little more margin above the amps power rating. Will R parts give the speaker more power handling.

More searching didn't reveal a direct comparison between the s and r models for the 10", but I did find the 12" s and r side by side in a catalog page. It's probable the the magnet on the p10s is smaller than the r, but the voice coil diameter is likely the same. So, putting r parts on the speaker (if that's what can happen) won't up it's output, but power handling is about heat. So I would think that the heavier gauge voice coil might up it's power rating. Also, modern adhesives do a lot for power handling too. But I'm no speaker expert. I can't actually find vintage catalog info on the p10r.?. It's interesting the a modern p10r is rated at 25W but the in the vintage catalog a p12r is only rated for 14W (the p12s is rated for 13W). With this info on hand I would have to guess that an actual vintage p10r was probably a 10W speaker (the p10s being rated at 9W). Not 25W like a modern p10r. But I don't know. But the point is that I don't think the wattage will be a problem. If four 10W p10r speakers could live in a cranked up Bassman I think your p10s will be fine in your amp. Especially considering any upgrade possible with the recone. But I'm out of my depth now.

[tigerzilly]

I got the 2.2mf cap and finished the recommended mod to the input. Also got the new Jensen speaker. Its sounds really good. Only issue now is vibration from the handle on top of the speaker cabinet. That may have been what I was hearing when I decided to put in a new speaker.

[tigerzilly]

I bought a roll of neoprene foam with adhesive on one side for my boat to seal the hatch. The extra has been serving me well for solving cabinet and chassis vibration issues. Works on the handle too.

[tigerzilly]

I discovered the best reason for keeping the old speaker. The amp won't fit in the cabinet with the new speaker. The. 5Y3GT is bumping up against the new speaker magnet before the amp is slid all the way back in.

[tigerzilly]

So back in with the old speaker. I doped up the rips and the outer edge of the cone. The new Jensen was louder and sounded good. The old P10S has early breakup with a more distinct sound. The handle rattle gave it the offensive noise. At least now the amp fits back in the cabinet as it should.

[Chuck H]

The standard fix for cone tears is layers of tissue and water resistant carpenters glue. The fix for edge surrounds is the heaviest tissue you can get and rubber cement. You seem to have done well enough as it is. And yes, the speaker depth thing can be annoying. The last amp I sent off my bench has the 5y3 just slightly inside the gap of the speaker frame. I had to rotate the speaker a quarter turn to achieve this and fortunately the cone doesn't whack on the rectifier tube BUT... I knew this going in and I checked the mounting depth of the new speaker before purchase. Figuring it might come to that. So you live and learn.

The MOD speaker is expressly said to NOT have a distinct tone. It's touted for modeling amps that include cabinet simulation so it's whole point is to have the frequency response to imitate most anything when certain frequencies are nulled rather than added. If you get my meaning. But people seem to like it well enough in several non modeling amps as well. Too bad it doesn't fit, but it's not a bad speaker to have on hand for a future project. So there's that.

Glad you like the circuit changes.