Traynor YGM-3 (early) - Selmer cab

[Barks]

Ok, goofed with my component order.

I thought I had 1R already but they turn out to be 10R at 1/4watt.
Can these still be used?

[rp]

Yes. You just move the decimal over. In the old days they would use 10 ohms as accurate 1 ohms where hard to find. 1/4W is sufficient here (it's practically a fast bow fuse ) but it should really be 1/2-1W only to keep it from failing before the real fuse blows. IOW it'll do for now.

[Barks]

Thanks - will put it in now.

One thing I'm learning here is the size of component stock I'll need to accumulate!

B

[Barks]

That was fiddly.

Continuity checked between all connections and all seems good.

here it is:

[IMG575]http://i650.photobucket.com/albums/uu222/katbarks/Traynor%20-%20Selmer/IMG_20150718_203233049.jpg[/img]

[rp]

Don't forget to check that you have bias on both tube pins and it's in a good range w/ the trimmer w/o tubes in first. When you put the tubes in max the bias V on the trimmer.

I would have eliminated the wire and just spanned the resistors from the tube pin to the ground lug - cleaner, less chance of noise.

[martin manning]

I like it. The jumper wire is from screen R to screen R, current sense R's are are tied to the center ground lug. The only change I'd make is keeping the leads down on the chassis and away from the heater wires.

[Barks]

I measured the old 22k bias resistor when I removed it and set the trimpot/18K combo to the same measured value and marked it with a sharpie.

Just turned it on and it seems to be working/sounding fine.

Now I need to learn how the bias process works.

*I had a little scare when the meter was showing 9vac on the heaters and over 500vdc on the plate - then noticed the battery symbol was flashing. New battery and it's all back to 6.4vdc and 428!*

[Barks]

I like it. The jumper wire is from screen R to screen R, current sense R's are are tied to the center ground lug. The only change I'd make is keeping the leads down on the chassis and away from the heater wires.

Going to move them back down now.

[martin manning]

Basically calculate the current you want from a desired fraction (say 70%) of maximum anode dissipation for the tube, which is 12W: 0.7*12W/428V = 19.6 mA. With 10R current sense resistors you will see that as 0.196V on the cathodes. Screen current is included in cathode current, so you will actually be around 65%.

The anode voltage will come up a bit when you dial the current down, so you'll probably have to repeat the process once or twice.

[Barks]

just checking that I take all measurements from pin 3 and pin7?

As set with trimmer to be close to how it was with set bias.

Pin3 to ground and vdc at 428

V3 is 26.7 = 95.2%
V4 is 24.8 = 88.4%

av dissipation is then 91.8%

Turned the trimmer to increase resistence

vdc now 432

V3 is 20.4 = 73.4%
V4 is 18.8 = 67.7%

av dissipation is then 70.5%

does this seem correct?

[martin manning]

The voltage that indicates the cathode current is measured on the cathode pin 3, or on the non-grounded end of the 10 ohm resistors. Anode voltage is pin 7, where the OT leads connect.

Looks like you've got it now. How's it sound?

[Barks]

It seems to sound pretty good, though I can't run it too loud right now as we're past midnight over here.
It seems clear and dynamic at volume of around 5. I'm used to the breakup point and loudness kicking in after 6.
The amp is outside the cab at the moment - so the cabs response is not quite the same as there is a 19" open gap across the baffle where it would sit.
The older tubes I had in it were very different on the cathode measurements, so I put the new ones back in and they were much closer.
There are lot of variable to this!

[rp]

Well cut off my legs and call me shorty, 432V on EL84s! Worthy of the crazy Russian electronic nuts I posted about on the Garage. And the heck w/ 6V6s this thing is ready for 6L6GCs or EL34s.

What do we do now that the initiation's over? How about a master volume? New OT?

[martin manning]

Just to be clear, both anodes are at 432V? The best accuracy will come from using the corresponding anode and cathode voltages, and measuring the cathode voltage on the non-grounded end of the 10 ohm resistors.

By the way, what is the screen voltage now? It will have decreased slightly due to the screen resistors.

I suggest playing it for a while and then see what you think.

[Barks]

Well, at least it's less than 456!

I've just been reading around the web, and it seems that 428v was quite common on this amp.
The only scheme I can find for the older 3 input has the B+ annotated to 428v.

At this point I feel happy that it seems to be nearer to stock and to what others are getting. It's a start.

Just been playing it and it has increased clarity and tightness - very responsive. No weird noises or crackles. My ears are hissing now, and I ned to stop as I have some music to mix.!
That flubbiness has gone, as has the weird "farting"
It breaks up at around 6, but is really great at 8 but turning the guitar down.
Max volume is more or less there at 5-6 on the dial. It just gets thicker when pushed 7 upwards.

The real test of course will be on a gig - I have one in a weeks time, but I'll be on Rhodes.