Troubleshooting a '70 Traynor Voicemaster YVM-1 PA Amp

[David Root]

I don't do a lot of repairs but a good customer brought this one in. This is a later schematic, with the LTP PI, EL34s and 470 ohm 10W resistor instead of a choke. Same as attached schem but no choke.

Checked the tubes, all good. Resoldered two iffy connections in the PI, plugged in. DC voltages check out on the money.

Put 400Hz sine wave in to input #1, practically no overall gain even with the MV and #1 gain pot maxed.

Turned them down a bit and touched DMM + probe to PI entrance cap, whoohoo!!, big volume, pop & crackle, dit-dit-dit. Switched off.

The two 40+40 can caps appear original. The first one tests +60uF on both, the second one ~45 or so each. On switching off they both hold a charge, I had to discharge them to ground from about 350V.

I think those caps need to be replaced with a pair of JJ 50+50/500V. This is a bear because they are soldered to the chassis (!) Will have to cut them off somehow, maybe a Dremel cut off saw, as I don't have a 300W iron.

I did measure the OT primary DCR, 125 + 145=270R. Didn't measure the secondary.

Is anything else likely to be amiss with this old warhorse?

[Leo_Gnardo]

I think those caps need to be replaced with a pair of JJ 50+50/500V. This is a bear because they are soldered to the chassis (!) Will have to cut them off somehow, maybe a Dremel cut off saw, as I don't have a 300W iron.

Yes, given their age, a good idea to replace old filter caps. Before you spend all day chopping and chipping with your Dremel, perhaps an affordable addition to your toolbox should be made. Weller 80 watt "pencil" iron, about US$35. That's a big pencil but you can do chassis soldering with it, also an asset for build-from-scratch projects, or if you have copper flashing & gutters in need of repair. Need larger? Yes you can select 120W and even 160W irons. But I've gotten done everything that needs to be done with the 80W, including unassing those old filters from Traynor chassis. You'll be using 1 3/8" clamps to fit new caps. I'm not too impressed with the "can caps" made to replace the solder-tab types, seen too many failures. You'll be good with JJ, F&T, or Ruby there.

[David Root]

Thanx for the tip Leo, I'll look into it.

Update:: Is this the one? See pic, Weller Marksman.

[Blindog]

I use one of these from Hobby Lobby, I forget who recommended it to me.

I only use it for chassis soldering, it works great, and the price is right. Also, you can usually find a 20-40% coupon for any single item on their site as well!

http://shop.hobbylobby.com/products/100 ... on-487546/

Mark

[David Root]

Great, thanx for the info!

[trobbins]

Perhaps some 'maintenance friendly' mods wouldn't go astray, like a sense resistor for each output valve.

Switched speaker connections are prone to causing grief - if the owner only ever uses one speaker impedance configuration, then maybe soldering some semi-permanent wiring around the switch would give some more confidence. As would a small stopper on each output valve screen, and a fuse with the standby switch.

[Stevem]

What type of cap is it at the PI input, as Ciramic types can and do have the leads break loose in them, I have even had this happen on some orange drop type caps where the factor placed too much stress on them when they where soldered in and this will make for intermitants and tons of crakling noise!

[Leo_Gnardo]

Thanx for the tip Leo, I'll look into it.

Update:: Is this the one? See pic, Weller Marksman.

Yes indeed that's the one. Now with "don't say you can't see it" orange handle.

The cheaper 100W iron is cheap all right, read the reviews.

Big advantage of the Weller is its huge tip - it carries a lot of heat to the work. I have Weller guns 100 to 300 watts but they don't work on chassis because the mass at the tip isn't much. FWIW the Weller "pencils" are popular with stained glass artists.

[bruce egnater]

The insert contacts are always suspect. Connect a cable from send to power amp in to check.

[bruce egnater]

Also, filter caps will not cause the symptom you describe.

[rp]

Yes either solder gun or pencil. Pencil is more useful as you can use it around pickups on guitars. Don't buy the Radio Shack pistols they always burn out after half a dozen uses, get a Weller, but at that point as you'd likely have to order it get a big pencil iron.

Here's a trick, a whack with a hammer and a sharp narrow wood chisel will often knock that solder blob to the chassis right up, if you're lucky and the prep was lame it'll snap off the chassis clean as a whistle. Usually it's 2-3 whacks, and be careful not to slip or dig into the chassis as then it'll look like a reptile dentist went at it.

If you solder a new can in place over the 'scar' it'll be an invisible restoration. But if you solder a new one then you have a pencil or gun.... so never mind... but I always try the chisel first as half the time it works perfect.

I agree to avoid the expensive C-E twist cans if you can, but if this was an old Champ, Brown Princeton or Deluxe, Thomas Vox etc I'd go for the fun of a perfect restoration and solder in a can.

[David Root]

Thanx for your reponses folks.

The owner of this beast has a suitable soldering iron he will give me, so that helps out.

The PI entrance cap is a Philips polyester cap, see gutshot pic attached. Interesting mix of mustards and Philips caps.

Will also check out the OT secondary switch, thanx trobbins in Oz.

Bruce, thanx for your note about the send/return contacts, I should have thought of that as I have had problems with exactly that in other amps in the past. Will check it out today and report back.

Thanx also for your tip about chiseling off the solder blobs, rp, I have done that in the past but forgot about it. Oldtimerz, not Alzheimerz!

[rp]

Quick, harvest those mustards and replace with 716s before the owner comes over! And cop the Rogers tubes too!

[pops]

You can always leave the can in place and unsolder the leads and use separate caps instead of a new can. It means you will need to find a different place to anchor the leads, but it can be done fairly easily.

[David Root]

Sorry rp, no Rogers tubes, owner gave me some '70s GE 12AX7 and a loosely matched (3 mA) pair of Guijang EL34s labeled by Groove Tubes. And a perfectly matched long plate EI 12AX7 from maybe 78 or 88, which I put in the PI.

Those Rogers 12AX7s from the '60s are pretty good. Some are actually Heerlen Amperex labeled Electrohome, but the real Rogers with the r factory code made in Toronto seem to be as good and also much cheaper than Bugle Boys. Also usually labeled Electrohome, an old Canadian electronics brand.