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Fender tube amp with Ampeg reverb pan : which tube numbers to use ?

Messages
344
I have a Fender tube amp which had the original reverb pan replaced by an Ampeg reverb pan. The Ampeg reverb is said to be lower output than the Fender reverb pan. ( Edit : reverb pan model number is 4EB201B which Antique Electrical Supply website says is 600 ohms input impedance , 2250 ohms output impedance , and used in Peavey solid state amps)

To make the Ampeg ( edit : Peavey ?) reverb sound optimal in this amp, what tube numbers should be used in V3 and V4 ?

The Fender schematic calls for 12 A T 7 in V3 and 7025 in V4 , but to compensate for the difference in output between the different reverb pans should other tubes be used in either of these sockets ?


As a separate broader general question about reverb tubes , if using a Fender reverb pan what would be the effect of :

(1) swapping out the V3 12at7 and using 12ax7 or 12au7 ?
(2) swapping out the V4 7027 and using 12at7 or 12au7 ?

Thanks !
 
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Swarty

Member
Messages
1,130
I suggest you lose the Ampeg tank before you smoke the reverb transformer. The Ampeg is capacitor coupled, the Fender is transformer coupled. The input impedence on the Ampeg tank is probably about 200x that of the Fender. For the driver use a 12AT7 or 12AU7, but not a 12AX7/7025?/ECC83 as they don't have the current. For the recovery use whatever you want, but reallize you'll take a gain loss with anything other than a 12AX7 type.
 
Messages
344
Swarty, here's some additional information :

Opening the reverb bag and looking closely at the actual reverb pan in the amp , the model number is 4 E B 2 0 1 B which Accutronics website says means :


600 ohms input impedance (the letter "E")
2250 ohms output impedance (the letter "B")

Antique Electrical Supply website says this model number was the reverb used in Peavey solid state amps. Although previous owner said "Ampeg" perhaps he meant Peavey.

Swarty, does this additional information affect your advice , and could the reverb pan be safely installed into a 1960's Deluxe Reverb amp ?

Thanks
 
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Messages
344
Thinking this through, I wonder if an amp tech in the past 40 years may have installed the improper replacement reverb pan at the same time as installing an improper replacement reverb tranny, meaning both parts would not be in spec with the schematic but compatible and balanced with each other.

Numbers on the reverb tranny are 0 2 2 9 2 1 and 6 0 6 - 7 - 1 8 .
Input impedance on the non-stock reverb pan is 600 ohm.

What is the probability a creative amp tech with a lot of parts laying around might have done this sometime in the past four decades ?

I don't know much about transistor equipment, but the non-stock reverb pan apparently is from a Peavey transistor amp which if using a tranny might have also conceivably had the tranny removed and installed with the reverb pan into the Fender tube amp. This is just brainstorming on my part , but potentially an important detail.

If yes, installing a proper model number reverb pan might create a problem where none currently exists.

What do you guys think ?
 
Messages
344
Searching the internet after posting the tranny question, I see the 022921 reverb tranny is the proper model number for the mid-1960s Fender tube amps.

Going just by the model numbers , apparently the reverb pan and the tranny are indeed far incompatible.


 
Messages
344
The reply's recommended reverb pan model number "4AB3" is long decay two spring reverb. My ear is familiar with medium decay reverbs but has never knowingly heard the effect of a long decay reverb pan. How different a sound/feeling is a long decay compared to a medium decay ?

Also, how different a sound is a two spring reverb pan (Type 4) compared to a three spring reverb pan (Type 9) ?

I wonder if there might be a website somewhere demonstrating the differences in effect ?



Thanks
 

Steelyman

Member
Messages
37
A really nice upgrade from the standard Type 4, 4-spring 4AB3C1B long delay pan is the Type 9, 6-spring 9AB2C1B medium delay pan for Fender Reverb amps for about the same $$. Much more controllable and very lush imho. Doesn't get runaway sproingy when turned past 3 like the Type 4. When I first replaced the pan in my Twin Reverb with a Type 9, I couldn't believe the difference. No going back ever. I plan on putting one in my Vibroverb clone also.
 

Structo

Member
Messages
9,559
Be careful about using a 12au7 in some amps, it has a much bigger current draw than any of the other 12a*7 tubes.
Plus it only has a gain factor of 17-20 Mu.

I would stick with the 12at7 for that application and use a quiet 12ax7 for the 7025 spot.
 

Swarty

Member
Messages
1,130
A really nice upgrade from the standard Type 4, 4-spring 4AB3C1B long delay pan is the Type 9, 6-spring 9AB2C1B medium delay pan for Fender Reverb amps for about the same $$. Much more controllable and very lush imho. Doesn't get runaway sproingy when turned past 3 like the Type 4. When I first replaced the pan in my Twin Reverb with a Type 9, I couldn't believe the difference. No going back ever. I plan on putting one in my Vibroverb clone also.
Many, including myself find the 6 (3?) springs too wet sounding.
 




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