Centralab pot codes

[galaxiex]

Somebody did a nice job on those schematics!
I used to work on a lot of Yorkville stuff so I have a few contacts with the corp.
If you want to post some pics of the guts we can speculate about the parts that look original but don't match the schem.

Thanks g1, but oops, too late...
I decided to strip most of the circuit card and start over.

The mods done were fairly extensive and some original parts moved around to accommodate the mods.

I'll put up some pics when I'm all done with attempting to re-create the circuit/layout.

[galaxiex]

Our band used to play in Ontario a lot, they seemed to like us there.  A gig in Chatham I liked.

Canada had a huge import duty on guitar amps and PAs. like 50%.  SO Canadian bands used Traynor a lot, as it was home grown.  I saw a lot of Traynor over there. I liked Traynor.  Roomy inside, and built like a tank.

Traynor the company was always supportive.  Always ready with schematics or parts.  And I always felt you got a good deal of equipment for your dollar with them.  Can't go wrong with Traynor.  If you will, they were like the Peavey of Canada.

What year(s) were you playing in Ontario?

I've always liked Traynor gear.
They sure seemed to be one of the "good" companies.

[Enzo]

Played a lot of high school dances and some bar gigs in Ontario in the 1969-1973 era.  Sarnia, Windsor, over to Chatham, down to the Lk Eire north coast.  I particularly recall playing the William Pitt Hotel in Chatham.  The band was Universe.

[galaxiex]

That's cool Enzo. 

I'm assuming you were a cover band playing what we now call "Classic Rock".
Any originals?

[Enzo]

Nope, just playing what was hot on the radio.  Though we did have pretentions.  Our guitarist thought he was Jimi so we played things like Voodoo CHile and Foxy LAdy.  And of course Stairwell.  But we also plaid Allmans and some Yes.  I recall a nice medley of Long John Baldry's King of Rock and Roll with Elton John Take Me to the Pilot.

We did have an anti-war protest set of all originals, complete with costume changes and lighting effects, but it was not part of our bar act.

[galaxiex]

Stairwell?
Is that a song or a band?

What instrument did you play in the band?

Long John Baldry's King of Rock and Roll... man I haven't heard that for ages.
Loved the intro to that song (Conditional Discharge) on the LP.
I think I still have the vinyl around here someplace...

[Enzo]

It was the era of Zeppelin too, so everyone had to do a version of Stairway to heaven.   I always call it Stairwell to Heaven to be ironic.  I guess now 40 years later, my cultural references do not reach everyone.

[galaxiex]

Ha ha, stairwell. 

Ok, I've been working on this amp for some time now...
Strange problems, weird noises...

And the O/T is gakked.
I just removed it from the chassis and it has some weird resistance readings on the secondary.

C/T to one end reads 165 ohms and 116 ohms the other.
When I measure end to end my Fluke meter goes nuts and the display just flashes O/L. Yes, battery is good.
Tried a different meter (Radio Shack) and it reads 0.270K ohms end to end. 

If I use the Fluke and hook up center tap to either end and shake/bump the Tx the reading changes for a split second.

Ordered a Hammond replacement. 1750S

[Enzo]

Put your Fluke on resistance, then measure the side that measures without blinking.  Use clip wires so you don't have to hold them.  Now while it is reading, push the scale hold button, that stops autoranging.  Now that you have locked in the reading range, move teh wires to the connection that was blinking before.

0.270k is the same thing as 270 ohms.   165 and 116 add up to pretty close to that.

I suspect your meter was reacting to the inductance of the transformer and causing a tiny current spike which triggered its autorange.  And...blinking.

Another trick would be to short the secondary before measuring the primary resistance.


HAving said all that, it is normal for MANY output transformers to have lopsided resistance like that due to the way it is wound.

[galaxiex]

Thanks Enzo,
I put the Fluke on range hold and that stopped the blinking and got a reading. 278 ohms end to end.

I did not know that about the inductance current spike thing, so double thanks! 

Also tried the shorted secondary trick and that worked too. 

Here's the thing...
With the meter hooked up if I shake or tap the Tx the reading changes.
Jumps up to something over 300 ohms.

When this was in-circuit and amp warmed up,
if I took a voltage reading from the plate of V3,
at 3/4 volume and up the amp would make weird noises (screeching/whistling) and the voltage dropped on the plate.
Also the slight power Tx hum would go away and got a loud hiss from the speaker.

It does not do this when taking a voltage reading from V4 plate.

This is why I think the O/T Tx is bad.

I have tried different output tubes as well.
The bias needs to be readjusted for the other pair of tubes I have,
but the symptoms remain.

Schem is in post #12.

Edit;
Oh ya, this amp had a fire at one time.
The steel chassis shield plate above V3 is scorched/burnt pretty bad.
The V3 socket was replaced and some of the wiring.
Other wires nearby got kinda toasted too.