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Post subject: 1960 Super Tremolo Issue
Posted: Thu Dec 15, 2016 6:46 am
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Hello!
I have a 1960 Brown Super 5G4. Towards the end of the night at the last couple of gigs the tremolo gets really weak and ceases to function. It starts out fine, but after 2.5-3 hours it begins cutting out.

I am thinking maybe I have the bias set too high. IIRC, I'm running about 33mA. Since this amps is bias vary trem, could this be the cause? I've tried a few different preamp tubes, but the problem persists. I am running the volume around 7, so the amp is putting out some heat.

After I let it cool down and retry the vibrato, it works. Is there something else it could be? A faulty cap in the trem circuit, maybe?

Thanks for the input!


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Post subject: Re: 1960 Super Tremolo Issue
Posted: Thu Dec 15, 2016 3:23 pm
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You talk about 6G4 not 5G4.

Schematic show 448 V plate voltage . 70 % plate dissipation for 6L6GC = 46 ma
33 ma is cold bias not hot.
What is you plate voltage ?

Maybe power tubes specs change after 2-3 hours playing and bias become wrong ?
IMO caps are good or not. If you suspect caps, replace all the 3 caps , two 0.01 mfd and one 0.02 at the fist half of the 12AX7 vibrato tube.


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Post subject: Re: 1960 Super Tremolo Issue
Posted: Thu Dec 15, 2016 4:06 pm
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stratele52 wrote:
You talk about 6G4 not 5G4.


Actually, some 1960 (brownface) Super Amps were identified by their tube chart as a "5G4" as this photo clearly demonstrates......

Image

Note the "JH" date stamp......August of 1960.

As to the tremolo issue, it may indeed be a bias-supply problem or something within the HV system. However the first thing I would check would be the tubes related to the tremolo circuit. Swap in known good bottles at the V3 and V4 positions then see if the symptom you observed continues to manifest. If not, then you're back on the road. If so, it's time to pull the chassis from the cabinet and start troubleshooting.

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: 1960 Super Tremolo Issue
Posted: Thu Dec 15, 2016 4:27 pm
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I can't find 5G4 schematic, only 6G4


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Post subject: Re: 1960 Super Tremolo Issue
Posted: Thu Dec 15, 2016 5:52 pm
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A "real" 5G4 schematic is of no use.

The amp I mentioned is actually a 6G4 Super Amp but the tube chart was marked as the earlier variant. It's another of those Fender anomalies that arises periodically.

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: 1960 Super Tremolo Issue
Posted: Thu Dec 15, 2016 5:59 pm
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Thank you guys for the suggestions.
The amp is a JC date code with center volume. It has 5 preamp tubes. Def 5G4.
I have seen a schematic for a 6G4 with 5 preamp tubes, so I believe that's the one people use for troubleshooting.

I have swapped V3 and V4 with known good tubes. That seems to help significantly, but I suspect something else may be going on. Filter caps and bias caps are relatively new. I'm wondering if it's a signal cap in the trem circuit. Yellow Astrons still intact.

Plate voltage is 450 or 470- I can't remember at the moment. I'm running JJ6L6s in there. 30 watt dissapation on those.

The amp sounds great. Really hi-fi. I may swap V3 and V4 again and see what happens. I'm playing this weekend, so I'll give it a good work out and see.

I've attached a link tp a sample of the delicious vibrato and a link to a 5 preamp tube 6G4 layout.

Thanks for the help!



http://www.prowessamplifiers.com/schematics/fender/Super_6g4-Layout.html


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Post subject: Re: 1960 Super Tremolo Issue
Posted: Thu Dec 15, 2016 6:31 pm
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Sounds like the tremolo tubes (V3 and V4) need replacing. This amp has two 12AX7 (7025) tube type Vibrato-Tremolo circuit. No opto-bug, like later blackface Super Reverb.

http://ampwares.com/schematics/super_6g4.pdf


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Post subject: Re: 1960 Super Tremolo Issue
Posted: Thu Dec 15, 2016 10:32 pm
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Bottleneck wrote:
I have swapped V3 and V4 with known good tubes. That seems to help significantly, but I suspect something else may be going on. Filter caps and bias caps are relatively new. I'm wondering if it's a signal cap in the trem circuit. Yellow Astrons still intact.


Take a look at the cathode-bypass caps associated with V3 and V4. You may have a DC leakage issue.

The schem I have shows a B+ of 456 VDC and -55 VDC for the bias supply.

Arjay

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Post subject: Re: 1960 Super Tremolo Issue
Posted: Fri Dec 16, 2016 3:14 am
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Retroverbial wrote:
A "real" 5G4 schematic is of no use.

The amp I mentioned is actually a 6G4 Super Amp but the tube chart was marked as the earlier variant. It's another of those Fender anomalies that arises periodically.

Arjay


I know is no use, these amps are all same ( to fix ) to me, if I never see a amp and I can't found schematic, the amp do not exist :lol:


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Post subject: Re: 1960 Super Tremolo Issue
Posted: Fri Dec 16, 2016 8:19 am
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Another suggestion was a cap or a carbon-comp resistor in the trem circuitry is failing. This may be the culprit. There's a big yellow Astron near V3/V4 that may be going microphonic. I can tap on it with a chopstick and hear noise from the speakers.

Red arrow on the pic below.

Also, the 5G4 with 5 preamp tubes is bias vary trem, right? Is it utilizing the power tubes or signal through v3 & v4 to make the effect work?


Image


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Post subject: Re: 1960 Super Tremolo Issue
Posted: Fri Dec 16, 2016 1:36 pm
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The 5G4 Super Amp (the tweed version) does not feature the tremolo effect.

Arjay

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Post subject: Re: 1960 Super Tremolo Issue
Posted: Fri Dec 16, 2016 1:53 pm
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Bottleneck's brown Super Amp 5G4 have the tremolo effect :?


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Post subject: Re: 1960 Super Tremolo Issue
Posted: Fri Dec 16, 2016 2:55 pm
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You haven't understood a single word that I've typed while discussing this topic, have you?

:roll:

Arjay

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Post subject: Re: 1960 Super Tremolo Issue
Posted: Fri Dec 16, 2016 6:44 pm
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Bottleneck wrote:
Another suggestion was a cap or a carbon-comp resistor in the trem circuitry is failing. This may be the culprit. There's a big yellow Astron near V3/V4 that may be going microphonic. I can tap on it with a chopstick and hear noise from the speakers.

Red arrow on the pic below.

Also, the 5G4 with 5 preamp tubes is bias vary trem, right? Is it utilizing the power tubes or signal through v3 & v4 to make the effect work?



http://www.mylespaul.com/forums/attachm ... 1481901748

Need log-in privileges, to see photo. But, I agree. The Astron caps maybe leaking DC (vintage ones are known for this). Measure the VDC on the grid side of these coupling caps. Anything above 1-2VDC indicates that cap needs replacing.

Constant 1-2VDC on 12AX7 signal grids may lead to overheating it, after a long session... and loss of volume.


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Post subject: Re: 1960 Super Tremolo Issue
Posted: Fri Dec 16, 2016 8:13 pm
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BMW2002Ti wrote:
Bottleneck wrote:
Another suggestion was a cap or a carbon-comp resistor in the trem circuitry is failing. This may be the culprit. There's a big yellow Astron near V3/V4 that may be going microphonic. I can tap on it with a chopstick and hear noise from the speakers.

Red arrow on the pic below.

Also, the 5G4 with 5 preamp tubes is bias vary trem, right? Is it utilizing the power tubes or signal through v3 & v4 to make the effect work?



http://www.mylespaul.com/forums/attachm ... 1481901748

Need log-in privileges, to see photo. But, I agree. The Astron caps maybe leaking DC (vintage ones are known for this). Measure the VDC on the grid side of these coupling caps. Anything above 1-2VDC indicates that cap needs replacing.

Constant 1-2VDC on 12AX7 signal grids may lead to overheating it, after a long session... and loss of volume.



Can you see it now?
Image


Last edited by Bottleneck on Sat Dec 17, 2016 1:20 am, edited 1 time in total.

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