Music Electronics Forum

Go Back   Music Electronics Forum > Amplification > Guitar Amps > Maintenance, Troubleshooting & Repair

Reply

 

LinkBack Thread Tools Display Modes
Old 09-16-2006, 11:21 PM   #1
Member
 
Join Date: Jun 2006
Posts: 32
twin reverb problems

My '73 silverface twin reverb has no reverb. Tried new cables tubes etc. I do get the crashing sound when I bump the reverb unit but thats all. How do I check the pan to make shure thats not the problem. It did work when I got it but just failed some time without notice.

I checked voltages on the preamp tubes and they are all very high when checked against the AA270 schematic. I know thats not the right one but shouldn't it be a little closer than about 40v to 60v high at the plates? I suspect that the dropping resistors have drifted.

I would like to fix this problem and blaceface the reverb channel. Which schematic is the best one to follow? After that I'm going to experiement with the normal channel. First things first, what would be the first thing to check?
tubelovin is offline   Reply With Quote
...and now, a word from our sponsor:
Old 09-17-2006, 12:51 AM   #2
Lifetime Member
 
Ray Ivers's Avatar
 
Join Date: Jun 2006
Location: Connecticut
Posts: 442
Quote:
How do I check the pan to make shure thats not the problem.
Quick and dirty? Swap the cables and try the 'crash test' again; if you get no spring noise at all, either the drive transducer is bad or a connection has come loose.


Quote:
I would like to fix this problem and blackface the reverb channel. Which schematic is the best one to follow?
As per your suspicions, I'd also check the B+ dropping resistors too (an easy check to make)... and I personally would use the AB763 TR schematic with 47K PI plate resistors, but YMMV.

Ray
Ray Ivers is offline   Reply With Quote
Old 09-17-2006, 02:36 AM   #3
Senior Member
 
Tom Phillips's Avatar
 
Join Date: Jun 2006
Location: California, USA
Posts: 611
Why 47k Plate Resistors?

Ray,
This is the first I remember hearing about using 47k PI plate resistors in the AB763 circuit. I never thought of trying that and always just change them out to 100k & 82k when I do a BF conversion. Can you explain what you like about the 47k set up?
Thanks,
Tom
Tom Phillips is offline   Reply With Quote
Old 09-17-2006, 03:07 AM   #4
Lifetime Member
 
Ray Ivers's Avatar
 
Join Date: Jun 2006
Location: Connecticut
Posts: 442
Tom,

I've always liked 12AT7 PI/drivers in Fender amps, and I feel the 47K Rp's are a better match to this tube than the 82K/100K '12AX7 PI' values if you're looking for clean headroom - and if you're not, IMO you're better off using a 12AX7 PI with the TR AB763 values; just my $.02.

Ray
Ray Ivers is offline   Reply With Quote
Reply

Bookmarks


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads

Thread Thread Starter Forum Replies Last Post
Any thoughts on a UL Twin? dave////irongater Theory & Design 7 08-28-2006 05:32 AM
Pot Problems escyrs2000 Guitar Tech 4 08-17-2006 03:10 PM
Reverb mods for '70's Super Reverb Steve A. Mods & Tweeks 5 07-22-2006 12:22 PM
Super Twin distortion? drewl Maintenance, Troubleshooting & Repair 3 07-11-2006 04:22 AM
Slight problem with my Fender Twin Reverb. Humbucker Vintage Amps 2 06-13-2006 03:03 AM


All times are GMT +1. The time now is 12:08 AM.


Powered by vBulletin   Copyright ©2000 - 2009, Jelsoft Enterprises Ltd.
Content Relevant URLs by vBSEO