Hello everyone,
Not sure if I have a problem or not. I've got a 68 pro reverb that I've been pretty happy with, sounds good, no noise, reverb and vibrato function fine. Awhile back, I got a 79 Deluxe Reverb. I converted the PI to black face specs and removed the snubber caps on the powertube plates, and it sounds pretty good.
The Deluxe seemed pretty loud compared to the Pro. Made me wonder of the Pro was working as it should (even though it sounds really good) So I measured the Pro's output power using a scope. When I injected a 1000HZ sine wave into the Pro using a 6.2 ohm dummy load, I get a max clean wave of 12.2 VAC RMS, indicating about 24 watts of clean power. Dimed I get a big square wave of about 16 VAC rms which is about 41 watts. The Deluxe can get about 16 Watts clean and 25 watts maxed out. So the Pro is more powerful. But still, I would have thought the Pro could put out more power than it does. Just wondering what level of output power would be considered normal. I've tried a few different sets of powertubes, not much difference.
If you're having trouble sleeping the attached file contains voltage readings.
Would appreciate any comments.
Thanks
Mike
Pro Reverb output power
Moderators: pompeiisneaks, Colossal
Pro Reverb output power
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frankdrebin
- Posts: 131
- Joined: Wed May 14, 2014 11:40 am
Re: Pro Reverb output power
it also depends on OT,those pro were wimpy iirc.
285v plates at max power sounds like that,not to mention filtering,old and low value caps don't help.
285v plates at max power sounds like that,not to mention filtering,old and low value caps don't help.
Re: Pro Reverb output power
Thanks.
I have new filtering and also upped the reservoir with a couple of 220 UF (IIRC) in series wired to the hot side of the standby switch. This is probably the first time I've ever measured the DC on the powertube plates while a signal was being amplified. Not really sure what I should be seeing. There is some sag a the rectifier under signal conditions drops to 405 VDC from the idle voltage of 431 VDC.
I'm curious as to what the normal clean output power is supposed to be with the stock OT.
Thanks
Mike
I have new filtering and also upped the reservoir with a couple of 220 UF (IIRC) in series wired to the hot side of the standby switch. This is probably the first time I've ever measured the DC on the powertube plates while a signal was being amplified. Not really sure what I should be seeing. There is some sag a the rectifier under signal conditions drops to 405 VDC from the idle voltage of 431 VDC.
I'm curious as to what the normal clean output power is supposed to be with the stock OT.
Thanks
Mike
Sunnydaze
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Stevem
- Posts: 5144
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: Pro Reverb output power
What I can pass along for you is this .
My 1967 Bandmaster is made with the same OT as your 68.
My 67 has some 440 volts on the output tube plates with the way I have it biased.
This amp is/ was rated by Fender at 35 watts rms output, but with two NOS 1980 era Sylvania 6L6 outputs the amp will do a fully clean 38 watts.
This same amp biased the same but loaded with NOS GE 7581A output tubes will do near 45 watts rms!
The part number on your OT like mine should be 125AGA.
The six digit manufacturers code of numbers should start of with 606 which is the correct Schumacher made OT.
These numbers are taken through a 5.2 ohm load.
Note that these 4 tubes all test within 2% of each other on my twice yearly calibrated gm type tester, and by that I mean they all test up in the mid 90s!
Note that today's best new output tubes are Lucky to get to a 85 to 88 % test out on my checker!
If you want great nos tubes for your Pro than go to the SND tube site and purchase his 6BG6 Sylvania. Tubes and the adapter kits you will need to use them.
These tubes at some 22 bucks each for matched ones is a killer deal, so once you get the first two with the adapters being able to replace output tubes when needed for under 50 bucks and have them be NOS tubes is a God send!
A story that may be of interest to you would be what OT That I found came stock in my 1976 pro reverb.
Even back in the pre CBS era Fender would use the same chassis for many different model amps and just use tube block off plates if the amp being built up did not use as many tubes.
So for example my 67 Bandmaster has two unused output tube locations that would have been used in the Showman amp covered up.
The silver face amps that where a combo style with reverb and 2-12" or 4-10" drivers all used the same basic chassis.
I had always thought that the 76 pro reverb of mine never had the punch that it should so on the day that I got around to getting new outputs in it I also looked it over really good and at that point I took note of how large the OT was even in consideration that these where now rated at 75 watts rms!
In the test out I was shocked to find only some 37 watts of power and knowing that I just recapped the amp and a voltage check confirmed the needed output plate voltage I had some checking to I get down to!
To make a long story short in the end I found that the chassis OT wise was built up to be a 4 output tube twin reverb chassis, but finished off with just two output tubes!
In the end I wound up wiring the 2 drivers in series for a 16 ohm load and things then began to work out, but these Amps with the stated 75 watt output is joke as they can not do that number!
When I took the same output tubes that gave me near 45 watts rms in my bandmaster the best Clean Power I could yank out of it was 68 watts!
In regards to your amp what are your outputs idling at and also at the wattage output level where the output stage starts to clip what has your voltage on the OT center tap dropped down to?
My 1967 Bandmaster is made with the same OT as your 68.
My 67 has some 440 volts on the output tube plates with the way I have it biased.
This amp is/ was rated by Fender at 35 watts rms output, but with two NOS 1980 era Sylvania 6L6 outputs the amp will do a fully clean 38 watts.
This same amp biased the same but loaded with NOS GE 7581A output tubes will do near 45 watts rms!
The part number on your OT like mine should be 125AGA.
The six digit manufacturers code of numbers should start of with 606 which is the correct Schumacher made OT.
These numbers are taken through a 5.2 ohm load.
Note that these 4 tubes all test within 2% of each other on my twice yearly calibrated gm type tester, and by that I mean they all test up in the mid 90s!
Note that today's best new output tubes are Lucky to get to a 85 to 88 % test out on my checker!
If you want great nos tubes for your Pro than go to the SND tube site and purchase his 6BG6 Sylvania. Tubes and the adapter kits you will need to use them.
These tubes at some 22 bucks each for matched ones is a killer deal, so once you get the first two with the adapters being able to replace output tubes when needed for under 50 bucks and have them be NOS tubes is a God send!
A story that may be of interest to you would be what OT That I found came stock in my 1976 pro reverb.
Even back in the pre CBS era Fender would use the same chassis for many different model amps and just use tube block off plates if the amp being built up did not use as many tubes.
So for example my 67 Bandmaster has two unused output tube locations that would have been used in the Showman amp covered up.
The silver face amps that where a combo style with reverb and 2-12" or 4-10" drivers all used the same basic chassis.
I had always thought that the 76 pro reverb of mine never had the punch that it should so on the day that I got around to getting new outputs in it I also looked it over really good and at that point I took note of how large the OT was even in consideration that these where now rated at 75 watts rms!
In the test out I was shocked to find only some 37 watts of power and knowing that I just recapped the amp and a voltage check confirmed the needed output plate voltage I had some checking to I get down to!
To make a long story short in the end I found that the chassis OT wise was built up to be a 4 output tube twin reverb chassis, but finished off with just two output tubes!
In the end I wound up wiring the 2 drivers in series for a 16 ohm load and things then began to work out, but these Amps with the stated 75 watt output is joke as they can not do that number!
When I took the same output tubes that gave me near 45 watts rms in my bandmaster the best Clean Power I could yank out of it was 68 watts!
In regards to your amp what are your outputs idling at and also at the wattage output level where the output stage starts to clip what has your voltage on the OT center tap dropped down to?
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Pro Reverb output power
Steve,
Thanks. I think my problem was/is a combination of the tube types, lower wall voltage here in Taiwan and slightly higher than optimal dummy load ohms (6.2 ohms).
The Taiwan wall voltage is about 112 AC at 60 HZ I have some Sylvannia 6L6's that I tried after reading your message. Even with the lower Taiwan all voltage the Sylvania's can put out about 31 watts clean and 48 watts with the amp dimed.
FWIW the tubes that were testing low were barely used Sovtek 6L6wxt'S and used pair of SED 6L6's.
Kind of surprised by the difference. Still at lower volumes, the Sylvannia's are a bit darker sounding. Too late to play at any volume.
thanks
Mike
Thanks. I think my problem was/is a combination of the tube types, lower wall voltage here in Taiwan and slightly higher than optimal dummy load ohms (6.2 ohms).
The Taiwan wall voltage is about 112 AC at 60 HZ I have some Sylvannia 6L6's that I tried after reading your message. Even with the lower Taiwan all voltage the Sylvania's can put out about 31 watts clean and 48 watts with the amp dimed.
FWIW the tubes that were testing low were barely used Sovtek 6L6wxt'S and used pair of SED 6L6's.
Kind of surprised by the difference. Still at lower volumes, the Sylvannia's are a bit darker sounding. Too late to play at any volume.
thanks
Mike
Sunnydaze