It is currently Mon Mar 16, 2020 8:26 pm

All times are UTC - 7 hours



Post new topic Reply to topic  [ 56 posts ]  Go to page Previous  1, 2, 3, 4
Go to page Previous  1, 2, 3, 4
Author Message
Post subject: Re: Twin Reverb 135W low distrted volume
Posted: Thu Dec 08, 2011 11:27 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26417
Location: Tombstone Territory
I must caution you -- the pull-boost feature on the MV control never provided what could be termed a "dramatic" difference in tone. In fact, most players familiar with the UL amps ignored the boost function altogether. It's possible that whatever you're hearing with the boost engaged is all you're ever going to hear.

Just saying.

(as someone who has owned this identical amp since 1978......)

HTH

Arjay

_________________
"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


Top
Profile
Fender Play Winter Sale 2020
Post subject: Re: Twin Reverb 135W low distrted volume
Posted: Thu Dec 08, 2011 11:59 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
+1 Retroverbial

As far as the description of the output jack wiring, that all sounds right.

What the external jack should do is insert the external speaker(s) in series with the internal speakers, and at the same time switch to the 8 ohm tap on the transformer. The main jack uses the 4 ohm tap on the transformer, run through the switch on the external jack. So, I suspect that the external jack is actually connected to the chassis. The external jack must be isolated from the chassis, as the "negative" side of the external jack is connected to the "positive" of the internal speaker when just the main jack is used. If the external jack is connected to chassis, this would short out the main jack, but the external jack would still work. And, after rechecking the schematic, it appears that the external jack does normally work by itself, still being the 8 ohm tap.

Forgot to mention, that when the external jack is used alone, the feedback resistor/cap that are connected to the transformer secondary middle wire, are grounded. Not sure how that would sound, and would dump some of the PI grid voltage to ground. I would have to study this some more, but my feeling is to not use the external jack by itself, even though it works.

_________________
---> "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.


Last edited by shimmilou on Thu Dec 08, 2011 12:54 pm, edited 1 time in total.

Top
Profile
Post subject: Re: Twin Reverb 135W low distrted volume
Posted: Thu Dec 08, 2011 12:44 pm
Offline
Hobbyist
Hobbyist

Joined: Mon Sep 14, 2009 9:05 pm
Posts: 32
Shimmilou - YOU ARE THE MAN! (or woman I suppose, this forum doesn't show gender but I don't know too many women who are likely to be found in the inside of amps) So here's the deal - some previous owner of this amp has clearly removed one the rubber washers that isolates the external speaker jack from the chassis - the one on the outside is there, the one on the inside - gone. Removing the jack from the chassis solved the problem! I'll find a suitable replacement and re-install and all should be good. Thank you so much for hanging in there with me on this, you've been an incredible help. I also learned alot in the course of this adventure, I did buy one of the Weber books and read it cover to cover twice. I worked with tubes a fair amount in a day gone by, it's slowly coming back to me. I'll get this re-assembled and take some picks to post, the cabinet and grille cloth came out great as well. Of course it's also time to play through this amp for a while now that it's been ressurected - it's only fitting. Thanks again, Dan.


Top
Profile
Post subject: Re: Twin Reverb 135W low distrted volume
Posted: Thu Dec 08, 2011 12:53 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26417
Location: Tombstone Territory
shimmilou wrote:
it appears that the external jack does normally work by itself, still being the 8 ohm tap.


I can confirm that -- full power is available at 8 ohms impedance.

Arjay

_________________
"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


Top
Profile
Post subject: Re: Twin Reverb 135W low distrted volume
Posted: Thu Dec 08, 2011 1:02 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
Hey! Congrats danoHSS. :D

No, you da man, you picked up stuff so quickly, good job dude!

Retroverbial,

I edited my previous post to add the last paragraph. Do you see a problem using the external jack by itself, considering that this grounds the feedback loop (center wire of transformer)? And, after looking again at the schematic, using the external jack with the main jack unused, center wire of transformer grounded through the main jack, using half of the transformer, wouldn't what was previously an 8 ohm tap, become another 4 ohm tap?

_________________
---> "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 135W low distrted volume
Posted: Thu Dec 08, 2011 1:17 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26417
Location: Tombstone Territory
I believe so -- the tap apparently reverts to 4 ohms.

To tell you the truth, I've never even tried running only the extension jack before since such a configuration runs contrary to the typical operating parameters for a blackface or silverface amp. But I disconnected my amp's internal speakers, plugged a Showman cab into the extension jack, spun both volume knobs to "10", then blew most of the dust off of the window drapes in my amp room (v-e-r-y v-e-r-y l-o-u-d !!!).

I know this chassis is also used as the basis for the 1 x 15 Vibrosonic, which runs a single 8-ohm driver (either a JBL D130F or a Gauss PS15, depending upon the era). There is a wiring notation in the UL schematic that mentions this.

Arjay

_________________
"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


Top
Profile
Post subject: Re: Twin Reverb 135W low distrted volume
Posted: Thu Dec 08, 2011 1:34 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
Yeah, that threw me at first, I'm so used to seeing the "typical" Fender output jack arrangement that will not allow using only the external by itself. Goes to show how well the amp holds up when using it with the output shorted (very low impedance), that's what a shorting jack is made to do. At least it didn't melt. :lol:

Thanks for verifying that.

danoHSS,

These are the fiber washers that I use for isolating jacks from chassis. You'll need one of each, shoulder and flat for every jack that you want to isolate. You have to make sure that the threaded shaft doesn't touch the chassis either. The main jack is probably OK connected to the chassis since it is connected to ground anyway, noise would be the only issue, and isolating it might or might not matter for noise.

Shoulder:
http://www.mouser.com/ProductDetail/Keystone-Electronics/3069/?qs=l8Mz4RVwyflRu0gEeXTRvw%3d%3d

Flat:
http://www.mouser.com/ProductDetail/Keystone-Electronics/3222/?qs=zfzUrXoPZmiqhiSt05vgkw%3d%3d

_________________
---> "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 135W low distrted volume
Posted: Thu Dec 08, 2011 1:39 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26417
Location: Tombstone Territory
I learned something as well so it would seem that we all made out on this deal.

Plus dano's amp is once again up and running.

Congrats! And to all......

RAWK ON!

8)

Arjay

_________________
"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


Top
Profile
Post subject: Re: Twin Reverb 135W low distrted volume
Posted: Thu Dec 08, 2011 5:33 pm
Offline
Hobbyist
Hobbyist

Joined: Sun Nov 20, 2011 12:45 pm
Posts: 35
WooHoo! A success story for sure. Thanks for letting us hang in.


Top
Profile
Post subject: Re: Twin Reverb 135W low distrted volume
Posted: Fri Dec 09, 2011 9:24 pm
Offline
Hobbyist
Hobbyist

Joined: Mon Sep 14, 2009 9:05 pm
Posts: 32
Another quick observation - what I discovered is that a previous owner or amp tech had removed the offending line out/recording jack to replace the 25 uFd cap and resistor that sit directly below that jack and run from the tube pin to ground. They needed to remove the jack for access, clearly it did not get put back together correctly. Another thing I learned - there's a black fibrous (rigid) washer that goes onto the threaded portion of the jack from the outside back of the amp. This washer is designed to fit exactly inside the outer layer of the back plate (it's a 2 layer affair, the chassis body and a trim plate that contains the screen printing), providing 360 degrees of clearence between the threaded jack body and the chassis - it's an alignment washer - it fits tightly to the threaded shaft and perfectly into the drilled hole in the rear faceplate. Once this is in place, both the inside and outside need to be isolated from the chassis, but this rigid washer makes the alignment of the jack in the hole an easy affair.
Glad this turned out well and that we all had fun following and learning from it! Stay tuned for the next project - I've been seeking out total wrecks of older Fender amps to restore, this was my fourth success (although I've started looking at some old Gibson designs recently). Yes, I know I owe the forum some photos. I played through the amp for about an hour tonight, very enjoyable, extra special cuz I was able to bring it back to life after what was clearly a very tough past. Everything works, reverb, tremolo, etc - love these older Twins. Thanks again to everyone for the help and encouragement, Regards, Dan.


Top
Profile
Post subject: Re: Twin Reverb 135W low distrted volume
Posted: Sat Dec 10, 2011 12:26 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26417
Location: Tombstone Territory
danoHSS wrote:
I've been seeking out total wrecks of older Fender amps to restore.


Gawd, you're a glutton for punishment!

I don't mind some restoration or repair work but I really prefer to find them in as close to pristine condition as possible, like this......

Image

Rawk on!

8)

Arjay

_________________
"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


Top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 56 posts ]  Go to page Previous  1, 2, 3, 4
Go to page Previous  1, 2, 3, 4

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: