johnheath

Fender Deluxe vibrato problems
« on: January 12, 2019, 05:45:22 PM »
Hi all...

I am building a clone of the Fender Deluxe reverb for a friend. He bought a kit with everything from cabinet to the smallest screws.

It is done and working nicely except from the vibrato.

It is tube V5, a 12AX7, but it does not conduct properly. Both cathodes shows 0V. This the tube that involves the vibrato circuit with the optocoupler.

On the "bulb side" of this optocoupler the voltages read near some 380-400V which I believe is too much. Together with the 0V on the cathodes my guess is that something is wrong ;)

I have changed the tube three times with all brand new tubes so I am guessing that the tube is not the problem. I have also desoldered everything a couple of times. Strangely enough when I desolder the cable to the negative bias circuit I get some voltages on the cathodes of the V5.

So... I am suspecting the optocoupler to be the culprit, but the it is also brand new and I hope that I don't have to get another one?


Any Ideas?

ps. I could not upload the schematic

Best regards

/John
Nothing is impossible - It just takes some more time


alexc

Re: Fender Deluxe vibrato problems
« Reply #1 on: January 12, 2019, 09:47:46 PM »
Have you checked the 2M2 resistor in the feed to the negative bias cct ? Maybe it is gone 'low resistance' or even 'open circuit'.

Same with the 10M plate load resistor on the second half - maybe gone 'low resistance' ? 

Assuming your B+ feed is good, and your cathode ground circuits are good (not gone open circuit or high resistance), there's not much else really that would cause complete lack of current thru the (good) ax7.

The opto is probably neither here nor there to this problem - if it 'short circuits' you still have the 100K as a plate load. If it completely 'open circuits', you should still see some 'voltage transfer' to the plate from the 10M.

....

Incidently, you can use more modern opto couplers in this position quite easily ... there's nothing too special about the old style one .. just a led and a cs photo-resistor.

I tried a bunch of types, including 'heat shrinking' up my own with different color leds and such.

I think I ended up with a 'white led' of the modern variety and a cad-sulf photo resistor.

...

My 'ab763' build, a super reverb, still gives me grief in the opto trem circuit   ::) 

As far as I know, you need to be a really good craftsman in the wiring, around this area of the eyelet board, to get a circuit with the right amount of 'parasitics' to  'work right'.

Also, contrary to what I did, I think the old 'ceramic caps' are best in the osc -  first stage ax7.

Mine works fine, but after time 'on', and depending on the ambient temperature !  ...  it can get a bit 'helicopter-ish' at 'silence'.
Or the oscillation dies out and requires a 'foot switching' or an 'speed' tweaking to revive it's oscillations.

With 'tube rolling', I eventually found a reasonable ax7  that gave better perf  wrt these issues that I have. There was quite a bit of difference between choices, as I recall.

In my own diy case, when it works, it's great!   

I don't remember any particular problems when I used authentic Fender Twin Reverbs  silver face types ..

..

Anyway - I would confirm hv on the plates first, then confirm ground continuity at the bottom of the cathode circuits, and low resistance to ground at the cathodes.

Then check those two 'grid leak' circuits and go from there.

Good luck - interested to know how   you go.

« Last Edit: January 12, 2019, 10:11:10 PM by alexc »
I ping therefore I am

CJ

Re: Fender Deluxe vibrato problems
« Reply #2 on: January 12, 2019, 10:12:27 PM »
did you put in a foot switch jack?   failure mode for bad or non existent foot switch is no vibrato due to lack of ground in cathode circuit
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

alexc

Re: Fender Deluxe vibrato problems
« Reply #3 on: January 12, 2019, 10:27:39 PM »
Yep :)

And the shielding on the footswitch is important too  ...  need to make sure it's in good condition and not frayed or busted up.

And, check the tube socket isn't damaged (fairly unlikely) and properly wired (generally speaking),  and of course, it be 'glowing'.
« Last Edit: January 12, 2019, 10:30:52 PM by alexc »
I ping therefore I am

johnheath

Re: Fender Deluxe vibrato problems
« Reply #4 on: January 13, 2019, 05:18:40 AM »
alexi: Thank you sir for your input on this. I will have another go at it but I have checked the wiring over and over again. The resistors are "old" carbon comp and in the kit you just got the one that was expected but I can change them for metal film resistors.

Anyway I will report back when I get some results.

Best regards

/John
Nothing is impossible - It just takes some more time

johnheath

Re: Fender Deluxe vibrato problems
« Reply #5 on: January 13, 2019, 05:28:14 AM »
did you put in a foot switch jack?   failure mode for bad or non existent foot switch is no vibrato due to lack of ground in cathode circuit

Thank you sir

I will have a second look at it today and specifically check the groundings. But tell me I have read the schematics over and over through the years but particularly the last day ;)

I will try with the foot switch theory of yours but the kit didn't contain a foot switch... you have to get that one separately :D


Best regards

/John
Nothing is impossible - It just takes some more time

johnheath

Re: Fender Deluxe vibrato problems
« Reply #6 on: January 13, 2019, 06:11:39 AM »
Ok - an update

Using a foot switch solved the problem to the extent that the vibrato circuit now works, but there is a "ticking" sound that gets through to the speaker. The "ticking" follows the settings of the "speed knob"... i.e increases in speed when increasing the vibrato speed.

If I touch the solder junction of the 10MEG resistor/ Bulb side of optocoupler/ anode of V5 (6) with the DMM probe as if to measure the voltage this ticking stops but the vibrato still works... well, that is a wanted result so now I wonder how I could proceed to get rid of the ticking?... without having to use my DMM :D


Best regards

/John
Nothing is impossible - It just takes some more time

abbey road d enfer

Re: Fender Deluxe vibrato problems
« Reply #7 on: January 13, 2019, 06:25:38 AM »
It is tube V5, a 12AX7, but it does not conduct properly. Both cathodes shows 0V.
That seems to indicate two different issues, or a tube which two halves are both duff, or a missing B+.

Quote
On the "bulb side" of this optocoupler the voltages read near some 380-400V which I believe is too much.
It is correct though, since it takes its power from the 385V nominal rail.

Quote
I have changed the tube three times with all brand new tubes so I am guessing that the tube is not the problem.
Correct.

Quote
  I have also desoldered everything a couple of times. Strangely enough when I desolder the cable to the negative bias circuit I get some voltages on the cathodes of the V5.
Not strange at all; the vibrato defeat works by biasing the tubes into cut-off. When you disconnect the negative bias, the tubes operate normally. But does the vibrato work when you disconnect the negative bias?
Can you check the cath and anode voltages on both halves when the neg bias is disconnected? In fact, the oscillator should work and you would have a variable voltage on the anode.

So... I am suspecting the optocoupler to be the culprit, but the it is also brand new and I hope that I don't have to get another one?


Any Ideas?

ps. I could not upload the schematic

Best regards

/John
[/quote]
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

johnheath

Re: Fender Deluxe vibrato problems
« Reply #8 on: January 13, 2019, 06:55:20 AM »
Thank you sir...

I seem to have solved the problems with the cathode voltages due to grounding the vibrato foot switch connector... by using a foot switch. When I do so the cathode voltages appear reading some 17V and 1.8V... seems "normal" with one cathode resistor of 100k and the other 2k7.

I guess that when "switching" the foot switch i.e not grounding the 2M2 resistor the vibrato stops and the tube is no longer conducting (which seems to be the problem described from the beginning)???

Or... should the tube have these cathode voltages at all time? (trying to understand the circuit) :)

The grounding of the junction of the 2M2/ 1MEG/ 1MEG seems to make the circuit work.

This is how far I have reached at the moment... but having the described "ticking" issue.


best regards

/John
Nothing is impossible - It just takes some more time

abbey road d enfer

Re: Fender Deluxe vibrato problems
« Reply #9 on: January 13, 2019, 09:15:06 AM »
I seem to have solved the problems with the cathode voltages due to grounding the vibrato foot switch connector... by using a foot switch. When I do so the cathode voltages appear reading some 17V and 1.8V... seems "normal" with one cathode resistor of 100k and the other 2k7.
Schematic says 11V and 1.8V, but I don't think it is very significant.

Quote
I guess that when "switching" the foot switch i.e not grounding the 2M2 resistor the vibrato stops and the tube is no longer conducting (which seems to be the problem described from the beginning)???
That's correct.

Quote
The grounding of the junction of the 2M2/ 1MEG/ 1MEG seems to make the circuit work.
Can you hear it pulsating?
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.


johnheath

Re: Fender Deluxe vibrato problems
« Reply #10 on: January 13, 2019, 09:21:27 AM »

 Can you hear it pulsating?

Yes or... well it sounds more or like it like... tick, tick, tick, tick and so on. At the same rate as the speed of the vibrato. And as mentioned it stops as soon as I touch the junction between the bulb side of the optocoupler/ 10MEG resistor and anode (6) of V5 with the DMM as if to measure the voltage???

Best regards

/John
Nothing is impossible - It just takes some more time

abbey road d enfer

Re: Fender Deluxe vibrato problems
« Reply #11 on: January 13, 2019, 09:53:39 AM »
Yes or... well it sounds more or like it like... tick, tick, tick, tick and so on.
That's pretty normal; there's some cross-talk between the high-voltage pulses and the audio path. But it should not be a bother in use. In actual use, a guitar amp's S/N ratio is not very good in view of pro audio standards.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

Gus

Re: Fender Deluxe vibrato problems
« Reply #12 on: January 13, 2019, 09:54:16 AM »
Is it based on a AB763 schematic? I have not read the whole linked page yet
https://robrobinette.com/How_The_AB763_Deluxe_Reverb_Works.htm

Do you have just ticking or do you have ticking with vibrato?

Ticking alone might be reduced with wire length and routing.
To start wires that are parallel couple to each other better than ones that cross at 90 degrees



alexc

Re: Fender Deluxe vibrato problems
« Reply #13 on: January 13, 2019, 08:13:07 PM »
'ticking' or 'helicopter-ing'   - very endemic to the ab763 vibrato  as I said  :)

It's quite hard to get rid of   ....  and when you do, it is only temporary  :)  depending on ambient conditions (warmed up temp, external temperature  etc)

....

It's mostly wiring dress, wire lay  in the first place,  and also ceramic caps in the oscillator (first stage ax7).

After all that, choice of ax7   (in my case the crappy sino type worked best   :o)

And then, choice of opto .... the commonly available (modern)  standard 'bug' is imho the worst ...

..

In my own builds (not clone) ...  I used the 'harmonic tremolo' from the brown series   ... far superior in stability, tone and excitement  to the 'single ax7 ab763 type'   ..  but it needs 3x ax7s  :)   AND a proper low-cut filter taken from the Vox ac30   

...  but the rewards are there all right. It sounds so hugely good

....

The 'ground' provided by the 'footswitch' for the tremolo section  is critically important   ....  needs to be as good as possible, continuity and low-resistance wise.

I do know that properly wired ab763 tremolo does work properly and quietly  (without punch thru of the osc especially at silence)  ...
 
- but it takes skill in wire dress and soldering   with very close attention to the 'wiring guide' - you can find lots of pics of the 'silverface' era insides ...  zoom in on the tremolo section and it's wires   and try to emulate!
« Last Edit: January 13, 2019, 08:19:41 PM by alexc »
I ping therefore I am

johnheath

Re: Fender Deluxe vibrato problems
« Reply #14 on: January 14, 2019, 05:01:19 PM »
Thanks all of you....

The problem with the ticking sound was solved by some testing of wire layout and a shielded cable.

Thank you for the inputs.


Best regards

/John
Nothing is impossible - It just takes some more time

alexc

Re: Fender Deluxe vibrato problems
« Reply #15 on: January 15, 2019, 12:47:32 AM »
Good stuff ...  I just might have to try that too (some shielded wire!)
« Last Edit: January 15, 2019, 01:26:14 AM by alexc »
I ping therefore I am

CJ

Re: Fender Deluxe vibrato problems
« Reply #16 on: January 15, 2019, 02:41:18 AM »
there are some Fender schematics out there with a .02uf cap across the 10 meg probably to cover up layout problems as the early blackface stuff had no cap,

age might also diminish the ticking as the bulb and LDR get a little weaker,

a switch on the vibrato pot would be a cool mod otherwise the Neon/LDR burn 24/7 (well as long as the amp is on that is)  or just use the foot switch all the time,




« Last Edit: January 15, 2019, 02:44:38 AM by CJ »
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

alexc

Re: Fender Deluxe vibrato problems
« Reply #17 on: January 15, 2019, 02:54:34 AM »
Very good info thanks CJ :)

I also tried some vactrol I think ...  they did quite well with some adjustments.

I do confess, now I mostly use more of a 'tweed deluxe'  [6v6]  and avoid all the reverb and tremolo biz, glorious as they can be.

Keep on truckin :)
« Last Edit: January 15, 2019, 03:07:45 AM by alexc »
I ping therefore I am

johnheath

Re: Fender Deluxe vibrato problems
« Reply #18 on: January 15, 2019, 06:05:46 PM »
there are some Fender schematics out there with a .02uf cap across the 10 meg probably to cover up layout problems as the early blackface stuff had no cap,

age might also diminish the ticking as the bulb and LDR get a little weaker,

a switch on the vibrato pot would be a cool mod otherwise the Neon/LDR burn 24/7 (well as long as the amp is on that is)  or just use the foot switch all the time,

Thank you sir...

That might be a  good idea with the cap across the 10MEG? I will surely try that Before my friend comes to get his amp :) Just to see what happens and in the future I might lose that shielded Cable :D

Best regards

/John
Nothing is impossible - It just takes some more time

johnheath

Re: Fender Deluxe vibrato problems
« Reply #19 on: January 15, 2019, 06:09:30 PM »
Very good info thanks CJ :)

I also tried some vactrol I think ...  they did quite well with some adjustments.

I do confess, now I mostly use more of a 'tweed deluxe'  [6v6]  and avoid all the reverb and tremolo biz, glorious as they can be.

Keep on truckin :)

Yes, for personal Point of view I agree… loose the vibrato and reverb. It is a very good amp as it is without it... I have also experimented with decreasing the NFB a bit which I Think makes it a bit more responsive to a Tube screamer or similar… and yes of course crank it a bit ;)
Nothing is impossible - It just takes some more time


 

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