Search found 17 matches
- Tue Apr 02, 2024 5:29 pm
- Forum: Fender Discussion
- Topic: Deluxe Reverb power transformer change?
- Replies: 16
- Views: 1672
Re: Deluxe Reverb power transformer change?
It looks like changing the rectifier is a relatively painless way to lower the B+ in this amp. I took the following measurements without changing bias. Line=120VAC GZ34 B+=462V Icathode 24/28mA 5U4GB B+=450V Icathode 22/26mA I may try the MOSFET B+ reduction circuit described in this current thread ...
- Fri Mar 22, 2024 12:35 am
- Forum: Fender Discussion
- Topic: Deluxe Reverb power transformer change?
- Replies: 16
- Views: 1672
Re: Deluxe Reverb power transformer change?
Thanks Phil,
It looks like I may be able to use a 5U4 also. My power transformer should be able to provide the extra amp of filament current.
It looks like I may be able to use a 5U4 also. My power transformer should be able to provide the extra amp of filament current.
- Sun Mar 17, 2024 4:37 pm
- Forum: Fender Discussion
- Topic: Deluxe Reverb power transformer change?
- Replies: 16
- Views: 1672
Re: Deluxe Reverb power transformer change?
Update: I have been unable to sign in to this forum for a while but have been reading. I took the amp out to the gig last night and absolutely love how it sounds. My band mates were amused that I kept looking in the back of it (to be sure the plates weren't glowing). Perhaps a read through of this s...
- Sun Mar 03, 2024 9:06 pm
- Forum: Fender Discussion
- Topic: Deluxe Reverb power transformer change?
- Replies: 16
- Views: 1672
Re: Deluxe Reverb power transformer change?
This thing wants to run hot. with 120VAC line, the plate V is 455, when tubes are idling 26/30 mA with bias V -50.8V.
With the price of tubes throught the roof these days, I'd really like to make them last. Is there a relatively painless way to lower B+ down some?
With the price of tubes throught the roof these days, I'd really like to make them last. Is there a relatively painless way to lower B+ down some?
- Sat Mar 02, 2024 10:09 pm
- Forum: Fender Discussion
- Topic: Deluxe Reverb power transformer change?
- Replies: 16
- Views: 1672
Re: Deluxe Reverb power transformer change?
Thanks Sluckey, Makes sense. I'll do that when I get to my workshop tomorrow. My B+ dropping resistors have increased to 11K and 11.5K. Is it worth replacing them at this time?
- Sat Mar 02, 2024 6:04 pm
- Forum: Fender Discussion
- Topic: Deluxe Reverb power transformer change?
- Replies: 16
- Views: 1672
Re: Deluxe Reverb power transformer change?
Thanks Stevem, I did not see a part number for the Xfrmr on my schematics. I'm tuning this amp up after some repair work. My initial concern was the B+ voltage(s) seem high. At 120VAC, B+ is 478VDC/plates are 476VDC with 17mA bias current. This is with the grid voltage dialed back as far possible -5...
- Sat Mar 02, 2024 12:41 am
- Forum: Fender Discussion
- Topic: Deluxe Reverb power transformer change?
- Replies: 16
- Views: 1672
Deluxe Reverb power transformer change?
My second tube noob question. I'm putting it in the Fender amp section as it seems (to me) to be more historical than it is technical. Does anyone know if the PT turns ratio changed when Fender Deluxe Reverb changed from AB763 to AB868 circuit? I am aware of the heater winding center tap removal and...
- Thu Feb 29, 2024 3:56 pm
- Forum: Technical Discussion
- Topic: imbalance in output tube current - fender deluxe reverb
- Replies: 21
- Views: 557
Re: imbalance in output tube current - fender deluxe reverb
It's fixed! There was a broken wire at the connection to pin 7 of the PI tube. The wire insulation was covering the break inside which was touching intermittently, especially with probe pressure. Most of my measurements/experiments were conducted on the circuit board which likely did not disturb thi...
- Sun Feb 25, 2024 7:27 pm
- Forum: Technical Discussion
- Topic: imbalance in output tube current - fender deluxe reverb
- Replies: 21
- Views: 557
Re: imbalance in output tube current - fender deluxe reverb
PI grid voltages are unchanged with both .1 shunt and .001 coupling caps removed. Additionally removed 820 ohm neg FB resistor with no change. Very strange....
- Sun Feb 25, 2024 5:04 pm
- Forum: Technical Discussion
- Topic: imbalance in output tube current - fender deluxe reverb
- Replies: 21
- Views: 557
Re: imbalance in output tube current - fender deluxe reverb
Thanks for the ideas and suggestions. I didn't find any broken wires or connections (yet) but will double-check again today. I made some DCV measurements and it does look (to me) like the PI grids are the cause of the problem. I haven't quite wrapped my mind around how the LTPI works but from what I...
- Fri Feb 23, 2024 10:44 pm
- Forum: Technical Discussion
- Topic: imbalance in output tube current - fender deluxe reverb
- Replies: 21
- Views: 557
Re: imbalance in output tube current - fender deluxe reverb
What does it do when you disconnect the NFB? That reminds me... when I first starting checking resistors, I discovered the NFB was 82K instead of 820 Ohms. I thought I had found the problem, but replacing it didn't change the imbalance. Disconnected it today and no change in imbalance. I also put i...
- Fri Feb 23, 2024 1:42 am
- Forum: Technical Discussion
- Topic: imbalance in output tube current - fender deluxe reverb
- Replies: 21
- Views: 557
Re: imbalance in output tube current - fender deluxe reverb
Yes, the resistors were replaced in an attempt to fix the imbalance. All of the old ones had drifted way out of spec. I started with the 5% tolerance ones then incrementally changed the rest. Some of the DC voltages changed slightly but the output imbalance remained (IMHO) large. For the purists: Th...
- Thu Feb 22, 2024 10:15 pm
- Forum: Technical Discussion
- Topic: imbalance in output tube current - fender deluxe reverb
- Replies: 21
- Views: 557
Re: imbalance in output tube current - fender deluxe reverb
Yes. In this case the imbalance stays with the amp. Even the 4mA difference in bias current.
I only have one spare 6V6 right now but will have a new matched pair tomorrow to experiment with.
- Thu Feb 22, 2024 10:08 pm
- Forum: Technical Discussion
- Topic: imbalance in output tube current - fender deluxe reverb
- Replies: 21
- Views: 557
Re: imbalance in output tube current - fender deluxe reverb
Duplicate post... Doh!
- Thu Feb 22, 2024 10:07 pm
- Forum: Technical Discussion
- Topic: imbalance in output tube current - fender deluxe reverb
- Replies: 21
- Views: 557
Re: imbalance in output tube current - fender deluxe reverb
I will check the OT using ACV. I had ohmed the input side previously with each leg showing 220 ohms to the center tap. I know that doesn't tell the whole story. It seemed to me that the power tubes and beyond were acting as expected given that their grid signal(s) are being driven with such unequal ...