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Post subject: Dating my Fender Twin and sum general questions
Posted: Tue Feb 22, 2011 10:30 am
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Hi everyone ! I was recently given a Silverface Twin. No speakers, one output tube broken, one missing. I've done a general cleaning (it was filthy), cleaned all the pots, retentioned power tube socket pins, and replaced all tubes with JJ's. I've powered it on, played thru it and it works fine. I used an 8ohm speaker for about a 5 minute test. I ordered two Weber 75 watt speakers for it and they arrived today.
Coupla questions:
1. I'm unable to date it and here's the info I have (no date code on tube chart):
Chassis S/N: F095685
Tranny code: A013692
Pot code: 021857
2. The new power tubes I have are a matched quad set. I'd like to adjust the "output tubes matching" pot to a correct adjustment. Can you tell me how to make that adjustment (by ear or by meter).
3. I noticed when I had the master vol up and the normal or vibrato vol up, there was no sound, until I raised either the treble, mid, or bass controls. Works the same on both channels. Is this a normal circuit design for this amp ?
4. Is this amp considered a 100 watter ?
Thanx much for your time and assistance, as it's greatly appreciated !


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Post subject: Re: Dating my Fender Twin and sum general questions
Posted: Tue Feb 22, 2011 11:13 am
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From the serial number info here, your amp dates to 1980......

http://www.superiormusic.com/page195.htm

On these late-model silverfaces, you do need some "tone" dialed in before the volume control(s) have any effect. My '78 is the same way and it's been like that since the day I bought it new.

Your amp is of the "ultra-linear" variety -- rated for 135 watts RMS. Don't ever expect to see that though. The best I've ever measured on a bench was 122 watts with a fresh set of Westinghouse glass and the bias set correctly. It's still plenty LOUD though. Once of the unadvertised features of this amp is the multi-tap secondaries on the output tranny, with self-switching speaker jacks. You can safely run a variety of speaker loads with this amp, from two ohms to eight ohms.

Best of luck, HTH

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Dating my Fender Twin and sum general questions
Posted: Tue Feb 22, 2011 11:50 am
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Hi Arjay....thank u for the quick response on the year and the "tone" circuit volume questions. Personally, I wouldn't have bought this amp, mainly because it's too much wattage for me. Even tho it was free, it still cost me bout $400 to get it goin. It's cleaning up very nice and seems to of had little use or at least was decently cared for. The Webers I'm puttin in it tonight are the Silver bell and the Blue Bell (each 75 watts, 8 ohm). I'm lookin forward to playin thru it tonight.

Any thoughts on adjusting the "output tubes matching" pot ?

Also, is this 1980 amp, one of the circuits that's really not supposed to be much of a "desired" sounding amp ?


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Post subject: Re: Dating my Fender Twin and sum general questions
Posted: Tue Feb 22, 2011 12:07 pm
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Nonsense.

These amps, while not possessed of the even-order breakup and harmonic compression of other vintage Fenders (none of the TR's really did this to any substantial extent in any case), are noted for being extremely loud and extremely clean platforms. Let your pedalboard effects drive your tone and use the Twin as a "linear power amp". And avoid using the pull-boost switch on the MV control -- they really squelch the tone out of the amp.

The "output tubes matching" control basically balances one pair of 6L6's against the other at idle, rather than performing as a true bias adjust pot for all four tubes (ie: you're only adjusting one side of the output stage). In any case, these UL amps run extremely brutal plate voltages -- in excess of 490 VDC. Let that be the determinant factor when calculating the 70% max plate dissipation figure. Due to the dynamics of this chassis, only the hardiest of 6L6GC's should be used. Sov-Teks and Tung-Sol re-issues would be a wise choice.

HTH

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Dating my Fender Twin and sum general questions
Posted: Tue Feb 22, 2011 12:37 pm
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Arjay, thanx again for the response. That's good to know that the amp should be a decent sounding amp. Since I ordered and received a complete set of JJ Tesla tubes already, I'll hafta go with those for now.

Could you elaborate more on how to perform the actual adjustment of the "output tubes matching". I'm comfortable (and cautious) working around lethal voltages. Now that I know the year (1980), I'll go look for the correct schematic. Currently I'm looking at a 1971 schematic. Do I need to look at a specific pin (ie; between pin 3 and ground) on each of the pair of tubes (two outside tubes vs the two inside tubes) and at least set the adjustment to get one "pair" of power tubes as equal as possible to the other "pair", using the backpanel pot adjustment ?


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Post subject: Re: Dating my Fender Twin and sum general questions
Posted: Tue Feb 22, 2011 5:01 pm
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Here's the schem for the ultra-linear models......

http://web.archive.org/web/200610200955 ... _schem.pdf

As you can see, you'll be balancing V7 and V8 against V9 and V10. The procedure is as you've surmised. Check your plate voltages first and use extreme caution of course. The Tesla's should be perfectly suited for this application. The only tube I'd be leery of would be the winged C's since they tend to meltdown at anything beyond 475 volts.

HTH

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Dating my Fender Twin and sum general questions
Posted: Wed Feb 23, 2011 9:54 am
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Well, I got the amp back together last night. She really cleaned up well for a 30 year old amp. All's left is clean an reinstall the tilt back legs. It's missin the lower back panel, so will either need to make one or find one. It sounds great, everything works and there's no scratchiness in any of the pots (WD-40'd em). I'm gonna leave it on for an hour or so today and let it bake. The tranny only just gets warm to the touch, so all seems to be workin fine.

After repairing the odds n end tolex tears with shoe goo (applied with a toothpick), scrubbin the tolex with a toothbrush, I used black dye to redarken the tolex, a little armour all, replaced all the chrome (amp corners, chassis straps, handle caps) and wow, it looks almost new. Also cleaned the front grill material (windex and light scrubbin). I kept all the old hardware in case someone would want that on down the road. I suspect someone might want to keep the amp just as it was; tears, smokey lookin grill, rusted hardware, bindin casters an all. But, a coupla years from now, it's get back some of it's road scars, dust, an grime on it again. :)

Thank you for the schematic Arjay and the assistance you gave me as that's very appreciated. All I had to do was tweak the "tubes matching" pot bout an 1/8th turn. Also noticed the hum I had went away, so apparently I can adjust this by ear in the future as tubes change a bit in power. P.S. I don't think I'm gonna haul this around too much....it's as heavy as an elephant ! :)


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Post subject: Re: Dating my Fender Twin and sum general questions
Posted: Wed Feb 23, 2011 10:35 am
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MLB wrote:
P.S. I don't think I'm gonna haul this around too much....it's as heavy as an elephant!


Ya think?

:lol:

Heavier still with a pair of JBL D120F's or Gauss PS12's!

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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