OffsetGuitars.com

I can actually turn it up to like three or four. My Ultralinear one I can barely get over one... LOL

Beautiful, looks just like my ‘76 TR.

How are those speakers? I’ve got Eminence Red White and Blues in mine and its basically a PA system. Tried to tame it a bit with a 12AX7 in the PI, but the difference is subtle, and it can bury my friend’s 5150 without effort.

Been thinking of trying out some Weber Chicagos, but not convinced there will be much of a difference.

There isn't any way I would pick out these random pair of speakers on purpose, but I actually like them. They were the ones it came with when I got them and I think they sound pretty good.

Nice, glad you’re enjoying them!

Would definitely recommend pulling the V1 preamp tunes and swapping out the 12AT7 in the PI for the 12AX7 you pulled out of V1. Like I mentioned above, the difference is subtle, but I do like the slightly more aggressive feel it gives to the Vibrato channel.

Haven’t really /cranked/ it and done an AB test versus stock (I like my hearing), but I’m enjoying the change. mostly run the amp at 4, with the MV at 10 (wearing earplugs, of course).

Congrats on a great score!

With the faceplate logo of "Twin Reverb Amp" and no master volume, that SFTR is much earlier than 1976. In checking the serial number, it dates as a 1969 manufacture. Ya dun good - now get those caps taken care of !

Ok, I'm going to be 'that guy' but it's for your benefit. That is a 1969 Twin Reverb.... I'm happy that you are enjoying it but that is considered the worst Twin Reverb of all time. Many years ago I bought a 1969 Twin with factory JBLs and I couldn't understand why it sounded so stiff and cold. I was bummed out after spending $1100 on it. (it was cosmetically nice and JBL twins were hot at this time). But... it was the best thing that happened to me as it really forced me to learn how to repair and modify tube amps.

So why is the 1969 Twin so bad? This is when Fender was experimenting with shortcuts to make production faster. The issue is the power tube ckt.
Compare pics of your amp's internal wiring near the power tube sockets to other twin reverbs from 1971-1974. You will notice that you have a bunch of extra capacitors (on a separate terminal strip by pwr trans.) )and high wattage resistors (those big gray-ish rectangle components on the tube sockets). All that extra crap is part of a wacky hybrid Fixed and Cathode bias ckt. The point of this was so you didn't need matched power tubes to run it. Cool idea but it made the amps sound terrible in most cases. I thought my 69 twin sounded like the worst solid-state amp I ever heard. Anyway, it can be converted to AB763 specs but it's a lot of work.

Originally people blamed the poor sound on big red coupling capacitors but they're fine.

I like the way it sounds. I also like the Ultralinear Twin though also and I know some people don't.

OK,
you have a Silverface twin with the infamous AB763.

Congratulations, you're halfway there. fix the bias circuit. Recap. done.

See those RCA 6L6's?
theyre worth more than you paid for the amp.

enough said.

Very nice. I have a 1978 ultra linear version and I love it. You get a great sound on the YouTube video!




I have had it since the early '80's and have had it re-capped recently and restored. No changes were made to the circuit but for beefier grid resistors.
Just to torture my back I had to replace the speakers and put in 2 of the best speakers I could find - EVM 12L by ElectroVoice.

I love the sound of Twins. Congrats on yours!! If you get hum, remember to balance the output tubes with a screwdriver if yours has this adjustment. Certainly on later ones they had hum and output tube adjustments. Any residual hum from the mains not filtered by the transformer can be balanced out of phase by the latter pot and the amp is totally quiet!

EDIT: OK I looked at the back panel of yours and these adjustment pots must have been added later.

Superb amplifier you have there!

Congratulations! From what I can tell, your amp is quite original in almost a bad way. Those white Mallory bypass caps are often replaced as routine maintenance. You haven't shown us pictures of the filter caps under the chassis in that pan. If those are original too then we're talking about an amp that hasn't been serviced in almost 50 years.

BlueSparkle wrote: ↑

Sat Jun 09, 2018 5:20 pm

OK,
you have a Silverface twin with the infamous AB763.

Um, do you know what "infamous" means? The AB763 circuit is the most common and popular iteration of the Blackface era. I get it, it says "AB763" on the tube chart, but the pictures of the circuit reveal that it is anything but AB763. Were there AB763 circuits in silverface clothes? Yes. But the AB763 circuit being "infamous"? Only for those Fender haters, I guess. Hey, maybe you just don't like Blackface tones. Nut'n wrong with that.

OffYourFace wrote: ↑

Sun May 27, 2018 12:49 pm

So why is the 1969 Twin so bad? This is when Fender was experimenting with shortcuts to make production faster. The issue is the power tube ckt.
Compare pics of your amp's internal wiring near the power tube sockets to other twin reverbs from 1971-1974. You will notice that you have a bunch of extra capacitors (on a separate terminal strip by pwr trans.) )and high wattage resistors (those big gray-ish rectangle components on the tube sockets). All that extra crap is part of a wacky hybrid Fixed and Cathode bias ckt.

I believe it! Going through Twin-Reverb schematics available online, this amp looks like it is the AC568 version. Like you said, those caps and those huge sand-colored resistors give it away. These caps and resistors do not appear in the subsequent AA769 and AA270 schematics, so those CBS engineers probably firgured out very quickly they weren't popular.

From one perspective, it's weird because I always thought 1969 was a not-so-bad year for Fenders - although Silverface, it's still pre-master-volume, and way before UL.

But from another perspective, as I understand it, CBS engineers first "modified" (messed with) the Twin Reverb circuit (their flagship!). Then those "improvements" trickled their way down to the others. Smaller amps like the Deluxe Reverb, Princeton, and Champ had very little change; though I see a cap on each power tube to ground on a SF DR schematic.



I don't know, from your video, the cleans sound great. Maybe it's when you crank it is when one can hear the CBS engineers' "modifications."

Maybe, not ripping out, but removing those caps and resisitors in the power amp section, and reverting to Blackface bias-adjust could be a start. But again, if you like it the way it is, then maybe routine maintenance is all it needs.

Good luck and HNAD!

Thanks! I will see what the amp tech thinks would be the best option. I don't mind it as is and I doubt I would crank it. I also don't mind if they think removing that change and making it more traditional either. Could always leave that stuff in and just disconnect them so it still sort of looks original.

Definitely 1969, going by the serial number: http://www.ggjaguar.com/fendamp6.htm

Finally looking into getting the caps updated and the power cord. I will see what Solderhaus thinks I should do about the bias capacitors. Will let you know.

Awesome - let’s keep this SF Twin thread going!

Just ordered some NOS preamp tubes for my 76, really excited to see how it changes things up to tonally.

Got a 1970 that sounds brilliant, but I have no idea if it’s got any of that bad crap in it. Huge sound with a ton of bass.