Traynor YVM-1...low volume

[TubeGeek]

I have a Traynor yvm-1 on the bench for a 3 prong cord and servicing.  One of the diodes has opened too.

The owner wants to use it as a vocal pa head. I think it may be better off as a modded guitar amp.  What do you think?

There are 4 unbalanced 1/4" inputs.  

Has anyone worked on one of these before? Any recommended mods?    Seems like it's a good candidate for tweaking.

[phsyconoodler]

Well since it was designed a s a vocal amp,get it working properly and see what it sounds like.
   The electrolytic capacitors should all be changed so he doesn't have any problems.Punt the crappy rectifier diodes and use some 1n4007's.
  Bias it up properly and there you go.It could be a guitar amp,but if he wants a vocal amp then let him have it that way.My .02 cents.

[TubeGeek]

Yeah, the electro's will be changed and like you said, new diodes will be installed.

Other than that I am curious if there are any mods that are popular with these.  The owner did say that he wants to use it as a vocal amp but is willing to explore other options.  Hence this post to get ideas.  

It seems to me that it is kind of out dated as a vocal amp because it has unbalanced mic inputs.  I'd think balanced xlr inputs would be the way to go???

I'm curious to see how it sounds too.  Maybe it's good as is and I'm getting over ambitious.

[DummyLoad]

i have been looking for one of those things for over 2 years now. with some very minor mods they scream as a guitar amp.

i used to search craigslist across all states with jaxed-mash until ebay sent them a cease and desist order on their CL search engine function. yay eatbait. :-\   

they do quite nice as a vocal amp as well. your customer should be happy once you get it sorted. happy hacking.

peace.

--DL

[PRR]

> out dated as a vocal amp because it has unbalanced mic inputs

If he favors SM58 mikes (who doesn't?), and isn't splitting into a "real" PA board, then get XLR-1/4" adaptors and wail. There is NO real problem with such a setup.

Fix the ground switch! ! ! Electrocuted singers are so annoying.

If he needs condensers with Phantom, it gets to be a Big Deal, and you should cut a deal with that curmudgeon for down-payment toward a nice used Yama or Peevey with XLR.

[DummyLoad]

and you should cut a deal with that curmudgeon...

hey! i resemble that remark! 

likely you won't like the band or the tune, however, the link below should give you an idea of what the YVM-1 can do with minor mods. the cabinet is a HI-WATT w/ four original fane speakers.

http://www.boxcarsatan.com/video-igotback.html

[TubeGeek]

I spent some time working on this amp last night...

I decided to leave the original filter caps in place and use empty eyelets to connect new filter caps in.  It turned out nicely, looks good too.  I replaced all the diodes and bias caps.  All electro's have been replaced.

While replacing the caps I noticed the wiring was different from the schematic I was referencing.  http://www.lynx.bc.ca/~jc/yvm-1.jpg  

After taking notes and drawing it out on paper, I went online and found a power supply modification for this amp.  This amp I have does have the mod already done.

My question is...is the power supply mod something I should leave in place?  

I am going to install a 3 pronger and remove the functionality of the ground switch and accessory outlet.  I am going to leave this amp as a vocal amp, no guitar mods.  PRR is correct, the owner wants to use the amp for band practice with 58's and 57's, so I recommended the xlr adapters to him.

[PRR]

> is the power supply mod something I should leave in place?

At this point, there's no real difference. Leave it alone.

Are you sure it is a "mod"? Basically it replaces a choke with a resistor (and moves the small-stuff tap so screen current in the resistor doesn't bobble the small-stuff). That sounds like something the _factory_ might do after building the first batch and realizing they needed to cut some more profit (lower cost) into the product.

[TubeGeek]

OK, will leave the PS as is.  I figured it was a factory mod/correction.

I have a bug to troubleshoot in the amp.  I plugged it in and it works but there is very low volume output.

Measuring voltage revealed an issue with the plate voltages on v1 and v2.  See voltages pic below please.

I double, triple checked the wiring and I cannot see anything obviously incorrect.  I replaced all preamp tubes...still measure low plate voltages.  I replaced the plate resistors and caps...still no change.  I measure 330 vdc on the filter cap side of the plate resistors and the low voltages on the other end.

I do measure a little bit of vdc on the grids of v1 and v2...will change out the caps.  The cathodes have 0 vdc too, could this be an indication of another problem?  I don't see any reference on the schematic what they should be.  I am assuming they should be around 1-2 vdc.

I am out of ideas.  

Where to look next?  Any guidance greatly appreciated.

[sluckey]

Measuring voltage revealed an issue with the plate voltages on v1 and v2.

All 4 plate resistors are 470K. I'd expect the plate voltage to be low.

I do measure a little bit of vdc on the grids of v1 and v2

The circuit is grid leak bias. There should be a negative DC voltage on the grids. Caps are probably OK.

The cathodes have 0 vdc too, could this be an indication of another problem?  I don't see any reference on the schematic what they should be.  I am assuming they should be around 1-2 vdc.

The schematic I'm looking at shows the preamps to be grid leak bias. The cathodes are tied to ground.

If all 4 inputs are low volume I'd suspect something after the master volume.

[TubeGeek]

Ahh ok Steve.  Indeed all 4 inputs have low volumes.  I'll do some more inspecting after the master vol.

Update...I checked over everything post master vol.  Nothing seemed obvious to me.  Is it ok to jumper the power amp input and mixer out?

[sluckey]

Is it ok to jumper the power amp input and mixer out?

Yes. If you look closely you'll see that they are jumpered when nothing is plugged in. Could be some dirty contacts though.