YBA-1 Guitar amp makes a chirp sound

[Gtr_tech]

1/2w is fine. If all you have is 1w, they'll work fine but its a bit overkill.

[Gtr_tech]

Those 220k's are bias feeds. Not the same thing.

AS far as that 4.7k, that is just a dropping resistor that feeds the phase inverter plates, It *should* be there. Look again....

[yba-1 user]

It is not there (I can put one in) but what will it change or help as far as function or sound?

[pdf64]

It will roll off the 'above audio' response and it doing so will mitigate for the type of issue you are experiencing. It's standard good practice to fit them.

[yba-1 user]

sorry, my chassis pic does show that it is there because I put it in when took the pic after studying the schematic- but it was not there when I first got it so I have been trying to see if it made any difference or not. right now it is not installed.

The wires that are connected to pin 5 on the tubes go straight to the master pot.

there is a pic of the chassis on the the thread above that was at 8:10 A.M.

[Gtr_tech]

I dunno why someone would omit that dropping resistor.....its not like these don't run a fairly stout plate supply to the PI and front end to begin with. So yer say'n there's just a wire in place of that resistor? Its prolly gonna be across 2 terminals of a can filter cap.

[J M Fahey]

Chirps usually (as in 95% of cases) spell oscillation/instability to me.
More precisely, the kind that does not run continuously but on some part of the wave.
You see a clean sinewave and at certain levels and frequencies, a subgroup of smaller amplitude but much higher frequency appears "mounted" on it.
You often even can't see the HV waves but their envelope, which is also what you hear as a chirp.
Yes, in some cases grid stoppers stop them; in other cases lead dressing is the key.
You really need a scope to catch them; going the ear-o-meter path is much longer.

[g1]

OK, it's starting to get confusing as we are back and forth between 2 separate issues that are getting mixed up.
a)missing grid stoppers. As suggested by Gtr_tech they should be installed. They are NOT shown on the schem. as they were added to the later models. Read his post carefully, he has explained exactly how to install them in SERIES with pin 5 on the power tubes.

b)missing R31 voltage dropping resistor in power supply. This IS shown on the schematic and should be installed.

R23 and R24 (220K) have nothing to do with either issue.

[jmaf]

Unsoldering V1's cathode capacitor was my idea to reduce gain. But seeing that photo, I see two things he could do before that: Substitute the green cloth covered wire from the jack to V1 A and B for shielded ones. Decide on a single ground point somewhere for the preamp... That can't hurt.

[yba-1 user]

Thanks for the input ....from all of you! I feel like I am narrowing this down.
So since my master is connected to pin 5 on the out put tubes....do I simply solder the resistor to the end of that wire and then to pin 5?

R23 and R24 were also remove when the master was installed...do they need to be put back ....but where since that is where the other leads are connected from the master?

[pdf64]

So since my master is connected to pin 5 on the out put tubes....do I simply solder the resistor to the end of that wire and then to pin 5?

That's it.

R23 and R24 were also remove when the master was installed...do they need to be put back

No their function has been replaced by the new master volume.

Substitute the green cloth covered wire from the jack to V1 A and B for shielded ones

Yes, those grids are within a couple of inches of the output sockets. However, despite that, it didn't cause an issue on the YB1A that I serviced last year. So do the output tube grid stoppers first.

Looking at the photo, have the power supply can caps been replaced recently? ESR in the B+ caps could result in oscillation at high gains, due to ineffective decoupling and resultant feedback paths.
Pete.

[yba-1 user]

yes those caps are new. What is-ESR in the B+ caps referring to?

I installed the resistors and everything seems O.K.

Might be just me, but it doesn't go as load as before....which isn't all that bad I guess.... but it makes me wonder if I am losing gain somewhere.
all in all it plays better - presence pot (high range expander) doesn't do anything or it does very little though.

[pdf64]

presence pot (high range expander) doesn't do anything or it does very little though

It won't unless the master is up high - who ever did the mod should have explained that?

[Gtr_tech]

Small value grid stoppers will have *no* effect of overall volume. They don't attenuate enough signal to notice. Its merely an isolation/filtering function they are performing.

[jmaf]

yes those caps are new. What is-ESR in the B+ caps referring to?

I installed the resistors and everything seems O.K.

Might be just me, but it doesn't go as load as before....which isn't all that bad I guess.... but it makes me wonder if I am losing gain somewhere.
all in all it plays better -

You won't notice any difference in loudness unless you've got the value wrong. What you might be experiencing is less hiss or high frequency noise, which makes you feel it is not as loud, but it probably is cleaner. Check the resistor color bands, if you felt a difference in volume maybe you put in a bigger resistor by accident. 1K5 to 5K6, even 10K won't do much for loudness, but will shape the tone a bit, not very noticeable either.

presence pot (high range expander) doesn't do anything or it does very little though.

"High range expander" was pretty creative. Looks like Traynor *really* didn't want his amp to be called a "'59 Bassman made in Canada"

But seriously, if your feedback polarity is correct, the presence pot should be effective. Check for a 4K7 resistance to ground from the feedback yellow wire going to the pot, check the pot, the capacitor, etc... The entire phase inverter network depends on that 4K7 to ground resistor(R20).