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Old 14th June 2007, 10:27 AM   #1
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Default Beard P100 Bias Lights

I've just acquired a Beard P100 power amp which had one blown output valve and the fuse holder on that channel was burnt out. I have replaced the fuse holder and found that the fault appeared to be dirty contacts on the valve holder as cleaning them up and replacing the blown valve has got the amp working again. There is still a strange anomaly on the amp though, when I crank the volume up the bias lights on the valve which was faulty don't light up as much as the other 3 - the volume has to be really loud for that light to go on. The amp sounds fine and I've tried swapping valves around and the same light always has the problem. The bias is set OK on all channels.

Is this a fault or just an anomaly that I can ignore?
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Old 14th June 2007, 12:02 PM   #2
poynton is online now poynton  United Kingdom
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The bias lights on my P100 do not light equally in operation so I would not worry.

If it ain't broke, break it !! Then fix it again. It's called DIY !
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Old 10th July 2007, 05:46 PM   #3
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I've found what I think is the cause of the bias light problem - the voltage across pins 1 and 6 (anodes) of V2 is zero on the working side but not settable to zero (using the P1 pot) on the faulty side. I suspect that one or more of the caps are faulty and since the amp is old I would like to replace all the signal caps. Since they are 1000V at 0.1 and 0.022 they obviously need to be decent quality - can anyone recommend a UK supplier - I've found a Canadian supplier but postage is expensive.
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Old 18th April 2008, 03:40 AM   #4
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Hi Dave,

I have been working with a Beard P100 for over 12 years now. I have had many amps both tube and solid state and somehow I always get back to the Beard.
Regarding the bias lights you should check the resistors across the pins of the power tubes, those are 10 and 270 ohms in value. When a tube blows usualy these resistors blow as well. Although the lights do not light together the difference between the lights on a single channel should not be that different.
I have worked on my Beard and have upgraded it a while ago which really bring this amp to compete with the best out there. I have done the following:
1. Replace the power filter caps with JJ 88uF 385V caps - can be found on Antique Electronic Supply.
2. Replace all resistors on the circuit board with Polyprop 1/2W 1% resistors. Mosts resistors in the P100 are 1/4w and change in value over time because of the high heat inside the unit. changing them to 1/2w will make the entire circuite more stable.
3. Change all signal path capacitor to ClarityCap and AuriCap types. This reallt improves the dynamics and low level detail of the amp.
4. Put filter caps (63V 1uf) across all valve heaters. Cleans the signal from some noise. A better solution would be to build a stabalizeds DC power supply for the valve heaters. I might do this in the future although it will be chalenging to find room to fit such a circuit in the P100.
5. Replace the Signal RCA connectors on the back and the Speaker terminals to high quality terminal this amp deserves.

With these changes I have yet to see an amp the Beard can not hold its own too.

All this was a lot of work and required disassembling the main circuite board which is complex but its well worth your investment. If you need the schematics send me a note as I have them with me.

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Old 18th April 2008, 11:28 AM   #5
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Thanks for the suggestions - I've since sold the amp but will bear your suggestions in mind in case I get another.

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Old 13th June 2010, 09:14 PM   #6
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hi ronash, i was reading your blog and found it very helpful, i was wondering weather you still had a circuit diagram for the beard p100, if its still available could you please email or send as a attachment please, my email add is , many thanks lou
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