Hadda have it. Saw 79 SF Pro Reverb. Had to. Mod and setting ideas?

[songsmith1950]

After I had that Princeton just the way I wanted it I made the mistake of going to the same music store and there she sat. 1979 Sf Pro Reverb. Same year as the Prinnie.

Had to. Played an earlier model in 70 thru 74 in the weekend job I had in a Legion hall that actually paid more for Fri and Sat nights than I made in my day job.

At any rate, I will now begin by blackfacing it. Then will do a few mods.

The most interesting mod will be the attempt at making channel 1 a 59 Bassman clone input. I can make it, I believe, use the chan 1 preamps to simulate the 3 amp before tone controls the Bassman and tweed Twin had.

Much more to do.

Any ideas? What has helped and made the great differences for your Pro Rev?

Also, gonna do the mod that allows interchanging 6L6's and EL84's.

Pro Rev Fans???

Tom

 

[sixty2strat]

Leave it alone .want a BF buy a BF fender....NOS tubes basis it right and the right speaker for you ears is all you need. Had mine for 6 years now paid 350 and it's a hell of an amp.....don't follow the part line on SF....it will break up very stonesy. swap 7025 and the 12at7 pi for 12ax7

 

[Wilko]

It would be very hard to BF a late 70's Pro Reverb (Maybe impossible).

Would need a new transformer and other bits for the tube rectifier circuit, as well as many other mods.
Those later Pro's are basically more like early Twin Reverbs. They don't sound like Pro Revebs at all.

 

[DrRobert]

Yeah, that has the ultralinear transformer set, which makes it a very different beast. OTOH it's not too valuable yet, so modding it won't hurt people's feelings too much. First thing would be good tubes and a new set of transformers...

 

[songsmith1950]

Actually from what a tech wrote somewhere here before, you can disconnect the screens from the output transformer, install the choke in place of the resistor in the power supply line and then hook up the screen resistors on the low side of the choke.

Gotta try that. Gonna do the choke anyway so might as well. The power tranny is not really a problem at all. It has plenty of power. If I do, or when I do change it I am also going to install the blackface Rectifier Tube circuit and 5U4.

The "boost" will be disconnected the first time I pull the chassis and I am going to leave the vibrato and reverb as they are. The Master Volume will be redone and converted into a Presence control.

I intend to use the two tube stages in the Normal channel circuit to work in conjuntion with the boost switch in that channel. What that will do is when the bright switch is on the two tube amp circuits will be used as a dual amp as in a Tweed Twin. The vibrato channel input will be taken through its usual first preamp stage, then through a two stage amp just as in the Tweed Bassman and Twin made up of the Normal stages. Then it will be injected back into the Vibrato channel circuit and proceed as always.

I am hoping this will give me a Pro Reverb Vibrato/Reverb channel with one amp before tones in the Vib channel and then a Tweed Twin/ Vib Rev three amp before tone when switching the bright switch on the normal channel on. I believe this can actually be fairly easily done.

In the long run I may install a Tweed Twin Low Power output transformer. At this time the power trannie for the same series will also be installed and the plate voltages lowered by the trannie and tube rectifier combo.

Very involved I know, but this is fun in addition to giving me what will be in the long run a form of Low Power Twin with vibrato and reverb.

If not I still love it as is. The cleans this thing puts out are wonderful.

Tom

 

[Wilko]

Right on Tom. Glad you know what you're up against and have a plan.

I just assumed that you saw that thread about Pro Reverbs and jumped in with the wrong amp!

 

[songsmith1950]

Many people do go after a late 70's amp like that thinking it is a 20 minute job to blackface it.
I was in error in one spot though. The power tranny may not be my first mod, but the fact that the voltages were much increased on those amps means it must be done to reduce the voltages to give the amp a warmer sound, with less gain and less headroom.
I will have to also install the tube rect completely from nothing. But I feel it is a worthy undertaking.
Again, my long term goal is to have an amp that can be Tweed Low Power Twin with reverb and vib or a Blackface Pro Reverb just by switching the bright switch on the then defeated norm channel bright switch.

Fun for sure, especially for a tech that has had to earn daily bread for the past 24 years by doing R and D for larger digital audio manufacturers.

Fun to get home, hit the basement, and crank up a few Fleming Valves!

Regards to all, from a EE who is stuck in the tube age on his own time.

Tom

 

[TT100]

Gotta hand it to you Tom. When I read your first post in the thread I backed out and slowly closed the door thinking "oops, he bought a UL and is going to be dissapointed."

You've got a great plan and that should be a very interesting PR when you're finished.

Kudos.

One thing though Lucy, you're gonna have a lotta 'splainin' to do if you try and sell it later!

Good luck and keep us posted!

:dude

TT

 

[songsmith1950]

Having studied the Pro Tube Concert schematic for a while it appears that all the 1/4 power switch is doing is disconnecting one of the high voltage windings from the power transformer to the power supply.
It would also have to add a resistor choice, chosen by the switch, to take the bias voltage on the 6L6's down from the nominal 63 or so down to about 25.8 or so for 1/4 power to run right.
I can't help but wonder if this mod might just help the "elevated high voltage" of the Ultralinear series to be tamed somewhat. After all it seems the higher tube plate voltages are one of the reasons the high gain is so much higher.
Have also considered going to cathode bias and installing a 30 watt rheostat in the high voltage line to make it possible to "brown out" the high voltage supplies while keeping ratios with the preamps and all intact. By the way, this would also allow use of 6V6's as well as 6L6's.

Are these wonders valid?

Nice thing about being a techie is that I can speriment with my amp and just fix it if I blow the hell out of it. And while fixing it, I will of course upgrade.

Tom