It is currently Mon Mar 16, 2020 7:36 pm

All times are UTC - 7 hours



Post new topic Reply to topic  [ 6 posts ] 
Author Message
Post subject: Twin Reverb SF Ultralinear 1980 tremolo (vibrato) woub woub
Posted: Fri Jul 29, 2011 11:27 pm
Offline
Hobbyist
Hobbyist

Joined: Tue Mar 15, 2011 4:22 am
Posts: 5
Hi*

At first the tremolo (Fender term vibrato) worked silent without
the woob woob woob woob. (Also I have an additional 0,01uF 600V
orange drop across the foto resistor stock from factory equipped.
But yesterday I plugged in the RCA switch (chinch) to activate the feature
and then I heared a plop as well as a cap would be discharged at once
and after this plop, now I have the the woob woob. The woob woob is not loud but it
sucks and it wasn't there before. The tremelo is still working but where
does this woob woob come from? I changed the oscillator tube but
nothing changes. The woub is faster or slower if you change the speed
with the speed pot. The woub woub becomes louder if you increase the intensity.
I checked the caps and the resistors and now only the Photoelement is left over.
Is there a possibility, that the photoelement is defektive? I don't know what to
check else.

The Amp is the SF ultralinear Twin.

Best regards
drstrange


Top
Profile
Fender Play Winter Sale 2020
Post subject: Re: Twin Reverb SF Ultralinear 1980 tremolo (vibrato) woub w
Posted: Sat Jul 30, 2011 12:49 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Yeah, I'd change out the opto-coupler resistor (cheap enough empirical try, anyhow). And hope for the best. The present opto-roach has an intact black cover?

BTW--- I once had a SF Bandmaster Reverb that had that irritating noise. After all was said and done, it was the wiring and soldering to the tube sockets that stopped the noise. Apparently, the position of the wires are critical to this stage. Esp the ones attached to the sockets. I have to thank Arjay, for that tip. :D


Top
Profile
Post subject: Re: Twin Reverb SF Ultralinear 1980 tremolo (vibrato) woub w
Posted: Sat Jul 30, 2011 4:44 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
Hi drstrange,

Just a thought, have you tried a new pi tube? :idea:

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


Top
Profile
Post subject: Re: Twin Reverb SF Ultralinear 1980 tremolo (vibrato) woub w
Posted: Sat Jul 30, 2011 9:54 pm
Offline
Hobbyist
Hobbyist

Joined: Tue Mar 15, 2011 4:22 am
Posts: 5
Hi*

Thanks for these hints
I know, that th wiring sometimes is bad on SF Amps but it was working.
I will check the Photoelement (20 Dollars!!) and also the PI which is new.

I saw also that the idle current of the PowerTubes is modulated if tremolo
is active without input signal, is this normal?

On my new RI Super Reverb I saw, that between the trem-footswitch and the cirquitry
there is a 10 kOhm resistor in series and a 390 kOhm resistor to ground to the 2,2MOhm
and the both 1 MOhm resistors.
This seems to me a voltage divider to make the footswitch not so hard switching.
Also in the Super I have a 4,7 uF Cap *with plus to ground because negative voltage*
parallel to the 390 kOhm resistor and I Think also this cap is used to make the
schematic more secure against the spike s of the switch. May be a spike of the switch
destroyed the photoelement?

The schematic of the super reverb with the additional parts is here on this page as pdf download:
http://www.fender.com/support/articles. ... schematics

What do you say to thos modification?
here in the SF the circut goes directly from the 2,2 MOhm to the footswich.
drstrange


Top
Profile
Post subject: Re: Twin Reverb SF Ultralinear 1980 tremolo (vibrato) woub w
Posted: Sat Jul 30, 2011 10:10 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
The Vibrato section of the amp is connected to the Bias Power Supply, without any isolation cap after the connection... so I guess it's possible that the vibrato is altering the negative voltage to the power tubes. You can test this by measuring the negative voltage at the bias power supply filter cap, as you change the vibrato settings. You maybe able to decouple this effect by replacing the 'lytic caps in the Bias Power Supply (if it's old). This is just a WAG.

As for your other suggestions... dunno. Prolly someone else on board as a better idea of their effects.

http://ampwares.com/schematics/super_reverb_aa270.pdf


Top
Profile
Post subject: Re: Twin Reverb SF Ultralinear 1980 tremolo (vibrato) woub w
Posted: Sun Jul 31, 2011 8:00 am
Offline
Hobbyist
Hobbyist

Joined: Tue Mar 15, 2011 4:22 am
Posts: 5
Might be. I changed the PI to blackface Spec and also I changed
the powerstage tubes and the grid resistors from 470 Ohm to 680 Ohm.
I see on the scope, that there is a wiggle on the BIAS. So I will equip a filter
cap *behind* the 2,2 MOhm to make the -52V stable against the wiggle
of the tremolo.
Also I will try several PI Tubes (I use a new 12AT 7 JJ) I will try also a
12AX7. Thanx from Germany for this HINT.
Nevertheless more advices are very welcome.

BR
drstrange


Top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 6 posts ] 

All times are UTC - 7 hours

Fender Play Winter Sale 2020

Who is online

Users browsing this forum: No registered users and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to: