Vibrato Chirp question

[mort]

OK, so I have the chirps in a '67 Bandmaster. I researched the topic and found this:

The solution calls for adding one capacitor and dressing the leads: Connect a 0.01 mf 600 volt mylar capacitor from the junction of the 10 megohm resistor (where it connects to the neon lamp on the eyelet board) to ground (where the LDR connects to ground also on the eyelet board). Dress the leads to the vibrato speed and intensity controls away from the tone controls and filter leads. Bunch together the leads connecting the components on the eyelet board to the tube socket of the 12AX7 vibrato tube.

Vintage Amps Bulletin Board • View topic - Vibrato "chirping"

When I went to try it I grabbed a .047uF by accident. It silenced the chirp but cut out the vibrato completely. The closest I have to a .01uF is a .02uF so I used that and now the chirp is silent and I have the vibrato effect. It does seem a little more subtle than what I'm used to from a Fender vibe but certainly usuable.

What I'm curious about is if I put in a .01uF will the effect be just a little more pronounced? And what is exactly going on here with this cap, what is it doing to fix the chirp and to diminish the effect when the value used is too high?

[mort]

Am I asking a really stupid question here?

[Zer09]

Am I asking a really stupid question here?

That cap installation filters the output of the oscillator. I had to do the same thing on my 60's Bandmaster and used .02uf. It worked and I was happy with the reult. Try the .01 or go as low as you can without the tick coming back.

[pdf64]

No, it's just tricky to come up with a suitable response; there's a lot of variables in a 45 year old amp and interference from the trem oscillator to other parts of the amp is almost always present to some degree.
However, the normal problem is a click rather than a chirp; a chirp indicates a higher frequency parasetic riding on the main oscillator signal.
Given that, I suggest you consider:
- the B+ caps 'fitness for purpose' and the general lead dress around the oscillator area
- other failing components, eg V5, oscillator caps/resistors, trem bug, oscillator cathode / bypass and plate resistor

The fix you've found may be a band aid that's masking the real problem.
Pete.

[Jazz P Bass]

I agree.
More observations will nail it.
A tick (normal problem) is certainly not a chirp.

[Zer09]

Mort,
Just saw your other thread on the restoration. Did you ever get the Normal channel sorted out and figure out why your volatges were off and why half of that preamp tube wasn't conducting? Your picures show that you replaced the filter caps and bias cap but what about the other electrolytics on the board itself?

http://music-electronics-forum.com/t28319/

By the way, you did a really nice job cleaning that chassis. That was one rough looking amp.

[mort]

Mort,
Just saw your other thread on the restoration. Did you ever get the Normal channel sorted out and figure out why your volatges were off and why half of that preamp tube wasn't conducting? Your picures show that you replaced the filter caps and bias cap but what about the other electrolytics on the board itself?

http://music-electronics-forum.com/t28319/

By the way, you did a really nice job cleaning that chassis. That was one rough looking amp.

Thanks. I actually just replaced a bad tube socket in V1 and that was the cause of the normal channel failure. It's up and running fully now and sounds great. The reason the voltage was high is because the pin 5 in V1 wasn't getting any voltage due to the bad socket. No current means voltage rides high.

The only other electrolytics that I have replaced so far are the pair of 25/25's that are near the center of the tag board(not sure the nomenclature for them). I didn't really notice any difference sonically.

http://www.cnjradio.net/fenderamps/b...763_layout.gif

No, it's just tricky to come up with a suitable response; there's a lot of variables in a 45 year old amp and interference from the trem oscillator to other parts of the amp is almost always present to some degree.
However, the normal problem is a click rather than a chirp; a chirp indicates a higher frequency parasetic riding on the main oscillator signal.
Given that, I suggest you consider:
- the B+ caps 'fitness for purpose' and the general lead dress around the oscillator area
- other failing components, eg V5, oscillator caps/resistors, trem bug, oscillator cathode / bypass and plate resistor

The fix you've found may be a band aid that's masking the real problem.
Pete.

All of the B+ filter caps are new. I do have a couple more trem bugs I could try out if need be. And would the oscillator cathode/bypass and plate resistor be the 100k and 25/25 coming off of pin 8 on V3?

[pdf64]

'All of the B+ filter caps are new'
Unfortunately that's not a guarentee that they're ok. Best to have a 'known good' spare available.
Even if the caps are good, on a rusty old chassis the grounding points may cause similar unwanted/unexpected positive feedback paths.

'would the oscillator cathode/bypass and plate resistor be the 100k and 25/25 coming off of pin 8 on V3?'
Pins 3 & 8
Pete.