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Old January 21st, 2009, 10:44 PM   #1 (permalink)
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new to me Silverface Twin - pics and questions

I purchased this from a guy off of craigslist this past weekend. It has a few issues (description and new twin-owner questions are below), but it basically works and sounds great.





Contrast, the big orange cat, checking the output impedance.


So, it is a '75 Twin Reverb with the push/pull master volume. The cabinet, speakers and grille cloth are from a newer twin amp, and it does have a few issues. However, the basics work, it sounds good like a twin should, and I got a good deal on it. So, I'm happy to have it! Now, on to the issues.

1 - Neither the reverb nor the vibrato work. When I put the reverb on 10, I can hear a faint beginning of reverb, but not nearly what it should do. I tested the reverb tank with another amp of mine, and it works great. So, it's something other than the tank. I can't get anything at all from the vibrato. The tubes for each of these are new JJ's. Could this be attributable to issue #2?

2 - No foot switch. Should I even expect the reverb or vibrato to work without it?

3 - Speaker mismatch. Ut-oh. The guy I bought it from was "restoring" the amp, and the cabinet and speakers are newer - maybe from a RI, I don't know. So, the speakers are 8 Ohms EACH, and the amp output is 8 ohms - TOTAL load. It sounds thin and trebbly and weird with one speaker plugged into each jack as pictured (I assume that's 16 ohms total load). If I unplug one, just running a single speaker at 8 ohms (as would be proper), it sounds really really good. The question is - how can I run both speakers? Should I wire them up parallel and run at 4 ohms? Will I blow stuff up like that? I realize that's a subject of some debate on here. I'll probably bite the bullet and get some new speakers (a pair of 16 ohms), but I can't do that at the moment.

4 - Crackly stuff. It buzzed and crackled and rattled pretty badly when I first tested it - hence the good price. However, I replaced the power tubes (which looked and supposedly were new) and tightened the speaker screws and viola - sounds about 95% better! There is still a bit of buzz when I hit certain bassy notes. My guess is that it needs a re-biasing and maybe a cap job. Or...maybe a new round of preamp tubes, although they look and supposedly are new. Whatcha think?

5 - Cosmetics. Yeah, I figure I can acquire proper chassis straps, rear panel and tiltback legs over time. And...should I even bother with a replacement MV knob?

Thanks for reading my rambling and checking out the photos. Y'all rock. All y'all, that is.

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Old January 21st, 2009, 10:46 PM   #2 (permalink)
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One more shot

This is what my music room (AKA wife's workout room) looks like with the new addition.

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Old January 21st, 2009, 10:55 PM   #3 (permalink)
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Re: items 1 +2 - Yes, you need the footswitch for those to work. I bet you dollars to donuts they'll be fine once you plug one in.

Nice looking amp!
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Old January 21st, 2009, 11:26 PM   #4 (permalink)
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Your speakers are wired incorrectly...they should be wired in parallel and only connected to the LH jack...do not use the extension spkr. jack like your photo shows....The Amp wants to see a 4 ohm load....2 -8 ohm spkrs. in parallel.
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Old January 21st, 2009, 11:37 PM   #5 (permalink)
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reverb works w/o footswitch, must have footswitch for trem to work.
twins are 4 ohm output. two 8 12's are right.

also stupid thing that might work, switch the in and out plugs on the reverb jacks on the back. it may just be hooked up backwards. i've seen that happen SEVERAL times, and it does as you describe. reverbs works but not very well.

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Old January 22nd, 2009, 12:09 AM   #6 (permalink)
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reverb works w/o footswitch, must have footswitch for trem to work.
+1

Whats the 1/4" jack to the right of the RCA's for the reverb tank? Some kinda addition....
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Old January 22nd, 2009, 12:34 AM   #7 (permalink)
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Mellecaster and Johnny: Thanks for the input! Yeah, I realize the speakers are wired incorrectly as shown - that's the way the seller had them wired, and I just snapped the photo when I got it home. Also, am I missing something about the load requirements? This amp is the 100W model (from the 70s) with master volume, and it wants to see an 8 ohm total load according to the back panel and according to the wiring diagram I downloaded here: http://www.ampwares.com/schematics/1...F_Twin_Rev.pdf. Am I missing something? I may be - fill me in!

Johnny: Yeah, I checked the in/outs for the reverb jacks. One way, it gives me the faint reverb (with the knob dimed) - the other way, nothing at all. I dunno... I'm going to get the foot switch at some point anyway, so I'll see if that makes any difference at all.

Umass: I'm not exactly sure what that is, although I've seen it before on other SF TR's of this era. Seems like I read somewhere that it's a line out, but it doesn't show up on the schematic I linked above.

Thanks for the comments guys - any further guiding light on the ohms thing would be appreciated. Hope my questions aren't too tedious!
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Old January 22nd, 2009, 12:54 AM   #8 (permalink)
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Quote:
Mellecaster and Johnny: This amp is the 100W model (from the 70s) with master volume, and it wants to see an 8 ohm total load according to the back panel and according to the wiring diagram I downloaded here: http://www.ampwares.com/schematics/1...F_Twin_Rev.pdf. Am I missing something? I may be - fill me in!
I may have answered my own question. Yeah, like you guys said - 8ohms + 8ohms wired parallel = 4 ohms (like the wiring diagram shows, right?). So, the 8 ohm total load would be if I ran an additional 4 ohm cabinet into the ext jack. Yes? Again, please forgive the ignorance.

Also, yeah - according to the Fender Amp Field Guide, this extra jack on the back is probably a line out.
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Old January 22nd, 2009, 04:00 AM   #9 (permalink)
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Althought unoriginal, the amp should be happy the way it's set up now. It wants to see a 4-ohm load, and that's what you'll get plugging 8-ohm speakers into the two jacks.

'Twere it my amp, I'd rewire the speakers, just because of OCD, not impending doom.

Enjoy your amp!

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Old January 22nd, 2009, 06:42 AM   #10 (permalink)
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This is the first time I have ever seen a schematic for a MV Twin, so pardon my ignorance, maybe one of you guys can explain it to me. But the print shows the OT running at 8 ohms not 4, and the ext jack wants to see 8 ohms which would run the OT at 4 if used. That is the way I am reading it anyway, maybe I am wrong. Also, it shows that the master volume switch interrupts the input of the reverb tank. So depending on whether he has the MV, pulled out or pushed in, the reverb will not work. But I could be wrong.
G-Yo,
Have you tried the reverb with the MV pulled out?
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Old January 22nd, 2009, 10:05 AM   #11 (permalink)
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+1

Whats the 1/4" jack to the right of the RCA's for the reverb tank? Some kinda addition....
Hum control (for amps that don't know the words). Around this time they started putting a 100ohm screwdriver pot there to to balance the filaments rather than use 2 100ohm resistors as a fake CT as had been done since '68 when the CT on the 6.3v winding went away.
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Old January 22nd, 2009, 11:41 AM   #12 (permalink)
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first off try replacing the 12at7 reverb valve with a quality one , also if i remember right the 3rd valve 12ax7 for trem swap with any of others to see if trem works. you will need the footswitch for trem , but you can just stick a phono in there which is linked together ie hot and earth joined , trem should then come on . if not open amp look for a heatshrink wrapped light and resistor on board and check its not shorting out anywhere. replacements are cheap enough anyway . good luck .
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Old January 22nd, 2009, 12:08 PM   #13 (permalink)
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This is the first time I have ever seen a schematic for a MV Twin, so pardon my ignorance, maybe one of you guys can explain it to me. But the print shows the OT running at 8 ohms not 4, and the ext jack wants to see 8 ohms which would run the OT at 4 if used. That is the way I am reading it anyway, maybe I am wrong. Also, it shows that the master volume switch interrupts the input of the reverb tank. So depending on whether he has the MV, pulled out or pushed in, the reverb will not work. But I could be wrong.
G-Yo,
Have you tried the reverb with the MV pulled out?
The output tranformer used is a 022889/125A29A --which wants a 4-ohm load (note that the Vibrasonic, which wants an 8-ohm load, uses a different OT.) There is almost *always* an impedance mismatch when the external speaker is hooked up to a Fender amp.

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Old January 22nd, 2009, 08:47 PM   #14 (permalink)
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I think your tank wires are reversed.

The 'vibrato' will work if you use something to span the center of the socket to the outside or ground. It could be something as simple as a unbent paper clip just to try it out.
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Old January 22nd, 2009, 10:44 PM   #15 (permalink)
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I bought a 73 Silver face twin a couple of years ago on the cheap, had a few things that needed to be sorted out, but I knew with the price I bought it for , there was going to be the price of restoring her to her former glory...Unless you reallly have all the tools, experience and electric gizmos to measure the roots of problems, do yourself a favor and get her checked out by an amp doctor, they are well worth it(these sweet silverfaces) and doc's not that expensive, doing this yourself could get you caught chasing a rabbit down a hole that is an endless maze
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Old January 23rd, 2009, 02:29 PM   #16 (permalink)
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Thanks for the input, folks!

Well, I wired the speakers up parallel and plugged them into the LH speaker jack. It works great, and what a sound. It's big and clear and loud, for sure. The crackling/popping has all but gone away, too.

Yeah, I tried the reverb with the wires both ways, and with the MV pulled out and pushed in. Same results (as mentioned above). It's not really slowing me down at this point, though. I have a decent reverb stompbox. Sometime soon, I will get the footswitch and check the vibrato, too.

I will most definitely take it to the amp doctor for a physical after I've gotten the pedal and new chassis straps. I figure it's probably due for a cap job at least, and maybe needs to be re-biased, and I'll let the tech do that. Anyway, it's sounds super sweet as is, and I haven't even spent anything other than the (very reasonable) purchase of the amp!
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Old January 24th, 2009, 11:00 AM   #17 (permalink)
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Man, that's great that you are giving another silverface a chance for new life...Back when I was using 4-12 cabinets(sweet bird of youth! What? WHAt? WHAT!!?)I sure could have used a thread like this to help me when I was rewiring stuff. For the money you just can't beat these old Silverfaces, plus they look like they can do battle anywhere, ...kind of like an old Nova or Toronado, you just never know what somebody has under the hood, but just having one says a lot about ones intentions and purpose
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Old January 24th, 2009, 12:18 PM   #18 (permalink)
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Have you tried a different (known working) RCA cable to the reverb tank too....?
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Old January 24th, 2009, 01:23 PM   #19 (permalink)
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Oh man, is this still going on? I just had the Trem go out on a early 1970's Traynor. The tremolo worked fine for years. Turns out the solder connection to the heater pin went bad, no filament power. All it needed was to just touch it with the iron, add a hint of solder, and PRESTO! So I am just wondering, are you sure the reverb driver is working, does it glow, have you replaced it with a working tube?
This must be something simple like that, or a connection went to ground somewhere maybe?. Someone above mentioned the RCA wires. I know you tested the tank with another amp, but did you use the wires from that amp or from this "new" SF Twin?
We aren't "throwing in the towel" yet, are we guys!!???
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Old January 26th, 2009, 02:54 PM   #20 (permalink)
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Oh man, is this still going on? I just had the Trem go out on a early 1970's Traynor. The tremolo worked fine for years. Turns out the solder connection to the heater pin went bad, no filament power. All it needed was to just touch it with the iron, add a hint of solder, and PRESTO! So I am just wondering, are you sure the reverb driver is working, does it glow, have you replaced it with a working tube?
This must be something simple like that, or a connection went to ground somewhere maybe?. Someone above mentioned the RCA wires. I know you tested the tank with another amp, but did you use the wires from that amp or from this "new" SF Twin?
We aren't "throwing in the towel" yet, are we guys!!???
Ha! Towel not thrown in yet. Backline & Wicked, good point about testing reverb with known working RCAs. I do know the tank works (as mentioned above), but I'll try new wires tonight. Also, the reverb tube does glow and look normal. I tried a different known working tube in its place and got the same results.

The tremolo - still sounds like I need to try it with a footswitch (rigged or otherwise) first before I crack 'er open and start messing with the wiring. It's not high on my priority list, but I'll update.

TS, thanks man! I'm happy to have it, and I intend to play lots of blues and indie rock with it. Now, I need to get off of my laurels and get a band going again!
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Old January 27th, 2009, 07:26 AM   #21 (permalink)
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Do you have an owners manual for it??? if not, go to Fenders web to download one. Most all fenders say "into a 4ohm or 8ohm load"
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Old January 27th, 2009, 02:26 PM   #22 (permalink)
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The reverb and vibrator will not work without a pedal, but there's a simple trick to make it work... Take an RCA cable, any RCA cable. Doesn't matter if it's working or shorted or anything, just anything with an RCA jack that you're willing to sacrifice. Cut the cable, about an inch from the end, strip the wire, and twist it together. Then plug that over the reverb footswitch jack and the reverb should work. Same thing will work for the vibrato too.
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Old January 27th, 2009, 10:41 PM   #23 (permalink)
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The reverb and vibrator will not work without a pedal, but there's a simple trick to make it work... Take an RCA cable, any RCA cable. Doesn't matter if it's working or shorted or anything, just anything with an RCA jack that you're willing to sacrifice. Cut the cable, about an inch from the end, strip the wire, and twist it together. Then plug that over the reverb footswitch jack and the reverb should work. Same thing will work for the vibrato too.
.

wrong.

a shorted jack will turn on the trem, but it will turn OFF the reverb
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Old January 28th, 2009, 04:21 AM   #24 (permalink)
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.

wrong.

a shorted jack will turn on the trem, but it will turn OFF the reverb
oops! sorry.
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Old January 28th, 2009, 08:21 PM   #25 (permalink)
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oops! sorry.
no problem, just trying to stop the proliferation of misinformation.
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