Foreplay 3 amp no output (Paramount)

Rob C · 269986

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Offline Rob C

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on: September 01, 2021, 05:45:00 PM
The board with 4 red LED's only one LED is lit and amp is not working. Tube glow, no output.  I tried swapping cables and tubes from the working 1 and I narrowed it down to the amp itself.   I inherited this setup from a family member. I am new to this lifestyle. But I have built guitar amps before. Thanks for anyhelp.
« Last Edit: September 01, 2021, 06:03:50 PM by Paul Birkeland »


Offline Rob C

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Reply #1 on: September 01, 2021, 05:47:48 PM
Some Pics


Offline Paul Birkeland

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Reply #2 on: September 01, 2021, 06:04:30 PM
This is a Paramount, not a Foreplay.

Do you have access to a meter to measure voltages?  They are listed in the manual, and measuring them and letting us know what they are will help us recommend what might need to be done to get your amp up and running.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Rob C

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Reply #3 on: September 02, 2021, 07:44:56 AM
I do have meters. Where do I test, and what voltages am I lookng for?


Offline Paul Birkeland

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Reply #4 on: September 02, 2021, 08:13:16 AM
You'd want to look in the build manual.  The terminal numbers are identified in the manual as are the expected voltages and how to measure them.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Rob C

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Reply #5 on: September 02, 2021, 04:46:40 PM
Cool thanks, im going to online search for the manual unless you can conveniently provide a link. Appreciated. Also, I'm guessing the center block is a preamp?
 I'm using 6ohm speakers with this setup. Is that OK?
The pot Infront of 300b is bias? I have some learning to do. Thaks for any help! Excited to hear these.


Offline Paul Joppa

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Reply #6 on: September 02, 2021, 06:23:11 PM
Yes, the center component is the Foreplay III preamp; surrounded by the two Paramount power amps. (Incidentally, that's the same setup I have.) Manuals in PDF form are available for purchase if you can't locate the original ones - older ones were on CD-ROM, newer ones are downloaded. The output transformers can be wired for 4, 8, or 16 ohms but triodes are not very fussy, 6 ohm speakers will work well with either the 4 ohms or 8 ohm wiring. The pot is a hum balance control.

Bottlehead amps are often modified; if you post pictures of the insides, it may be possible to identify the more popular ones.

Paul Joppa

Offline Rob C

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Reply #7 on: September 03, 2021, 08:04:21 AM
Cool thanks, I'm picking up the manuals today. What do the four red LED's indicate? Also the one amp that works isn't as loud as I would think. I can max the foreplay vol knob and it's still very audible. Is it meant for low volumes?


Offline Paul Joppa

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Reply #8 on: September 03, 2021, 08:29:14 AM
The LEDs are not used as indicators - they are "band gap" voltage references used in the current sources for the driver and its shunt regulator. If some of them are not glowing, it means the driver stage is not working correctly. The measured DC voltages, when you have them, will help diagnose the cause.

The amps put out 8 watts at maximum, and in my system at least, the Foreplay has much more than enough gain to drive the amp to clipping. Since I don't know the sensitivity of the speakers you are using, the output voltage of your source, or what exactly "as loud as you would think" means, I can't say much more yet.

One of the more common mods to a Foreplay is to reduce its gain, in cases of hair-trigger volume controls. It seems to me that might be a place to start - can you post a picture of the interior of the Foreplay?

Paul Joppa

Offline Rob C

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Reply #9 on: September 03, 2021, 10:35:26 AM
Foreplay


Offline Rob C

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Reply #10 on: September 03, 2021, 10:38:19 AM
Paramount guts


Offline Paul Joppa

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Reply #11 on: September 03, 2021, 01:12:15 PM
Neat and clean work!

Both the amp and preamp appear to be unmodified stock builds. As a first check, you can see if the Foreplay tubes glow (including the gas regulator in the middle), and the two LEDs underneath (one on each tube socket) are lit.

The Paramounts are version 1.0, without the so-called "soft-start" driver mod.

Next step is the voltage checks.

Paul Joppa

Offline Rob C

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Reply #12 on: September 03, 2021, 04:08:26 PM
When I did some troubleshooting before posting here.  the right channel works so what I did was swap all the cables on the side that I know is working to the left side. that did not work. I even swapped the tubes that were working, and the left side still didn't work. so I'm assuming it's not the foreplay but the left Paramount with issues.   On the foreplay I am getting in-and-out left and right signals but no signal from the left Paramount. I will be doing voltage testing in the next day or so day or so once I feel comfortable enough to turn it back on.


Offline Paul Birkeland

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Reply #13 on: September 03, 2021, 05:30:05 PM
That's great that you are able to get the manuals! 

Of most importance would be the DC voltages at all four pins on the 4 pin socket, as well as the DC voltages on the metal tabs of the two biggest transistors on the green C4S board. 

Just those 6 voltages would tell us a whole lot about what's going on!

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Rob C

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Reply #14 on: September 04, 2021, 03:05:01 AM
Awesome


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