YBA-1 Guitar amp makes a chirp sound

[yba-1 user]

I have an issue with my recently refurbished Traynor Yba-1 (1972)
It sounds OK until I hit a note on the high E string above the 12th fret. ( guitar)
At that point the note sounds more like a chirp than a musical tone.
It doesn't happen with all of the notes up on that register....just a few.
Is there a cap value or something I should look for on the tone stack?
I can post a pic of the chassis if needed.
I did lower the cap value on the volume control but that did not help. any Ideas

[jmaf]

Hi, and welcome to the forum.

Does this happen at any volume? Sounds like it's resonating with a few high notes. If it only happens at high volume, I'd try substituting or swapping preamp tubes around to see, it may be a microphonic tube.

If it happens at any volume, with any of the preamp tubes in any position, it could be a whole lot of of things. Sounds like you've been modding it, did you change any capacitor value before this started happening?

[yba-1 user]

It does the chirp at any volume. There were a few mods before I got it (master volume was installed) and to my knowledge the caps were replaced with the same value(s)

[jmaf]

I assume you have the amp open?

You could try unsoldering the cathode capacitor off V1 and see if the chirp goes away.

[pdf64]

The chirp could have several root causes / contributory factors. It's probably oscillation and increasing gain makes amps prone to oscillation, as does failing decoupling caps and poor lead dress.
There are quite a few versions of the YB1A. It would be beneficial to identify which schematic your amp best matches, see http://www.lynx.bc.ca/~jc/YBA1Schems.pdf
and also what work (service, repair, mods) has been done to your amp over the years.
Some detailed photos would help.
Pete.

[yba-1 user]

yba-1 user with chirping sound reply

Thanks for the replies
Mine is actually a 72' but it appears that it is more like the older version of the schematic from what I can tell.
here is the link to the schematic
http://www.lynx.bc.ca/~jc/661021_YBA1.gif

Here is what was done.
1. moved the standby switch to the back (where the ground switch used to be)
2. replaced the 2 prong with a grounded 3 prong.
3. installed dual gang master volume ( on hole left by moving standby switch)
4. replaced various caps

[Gtr_tech]

That version has no grid stoppers (in series with control grids) on the output tubes. I always need to install them for the amp to play nice with current production tubes. 1.5k-2.2k should do the job. The std value for EL34s is 5.6k, but I find that you don't need to go that high to have the amp run stable.

[yba-1 user]

O.K. now my lack of experience will show. (I held in there for a while) LOL
how would I go about fixing that?

[Gtr_tech]

Remove the wires on pin 5 of the output tubes. Solder the resistor onto that socket pin, then solder the wire you removed onto the other end of the resistor. Simple as that. Just make sure you insulate this with some shrink tubing so it doesn't contact anything....you could lose bias and melt the output section down. Its also a good idea to secure the wires to something nearby (*not* a plate wire) via wire ties to ensure the newly added stuff isn't allowed to flop around and possibly break off. That would be bad....

[Gtr_tech]

Oh....keep the leads on the resistors short. Leave just enough to loop around the solder tab on the socket. Same for the wire side...

[yba-1 user]

Oh....keep the leads on the resistors short. Leave just enough to loop around the solder tab on the socket. Same for the wire side...

Thanks I'll try that

[g1]

"It sounds OK until I hit a note on the high E string above the 12th fret. ( guitar)" Just in case, you've tried another guitar? From this exact description I would say fret buzz above the 12th on the high E.

[Gtr_tech]

That could very well be. But...these guys still need grid stoppers installed if there isn't any. All kindsa weirdness can happen if they're not there. The last one I did (YSR1) would motorboat violently in the presence of input signal. The stoppers cured it straight away....

[yba-1 user]

1/2 watt O.K or 1 watt ?

[yba-1 user]

It appears that there were grid stoppers that were there before the master mod.
if I am looking at the schematic right they are 220K r23 and r24.
If that is correct I wonder why they were removed after the master was installed.
Also I noticed a 4.7k resistor missing on mine r31?