Beard P101 amplifier.

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Chopsaw
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Beard P101 amplifier.

Post by Chopsaw » Sun Feb 02, 2020 1:24 pm

I need some advice regarding my Beard P101 amplifier. It has four output valves for each channel and mine was fitted with a mix of 6550s. One flashed over on one channel and blew the 1A fuse on that channel. I bought a new quad of JJ 6550s for the duff channel so now there's two decent quads of JJ valves. I haven't touched the amp or fitted the new valves because I've had other things to do but I started making a few enquiries and was told that this amp should really have original GEC KT88s fitted as these are the only valves robust enough for this amp. That's not really going to happen so I wondered if I could fit something like KT90s or even revise some component values so I could reliable use the 6550s. I think Andy who knows Nick quite well may have asked him to take a look at it or discuss it but I believe you (Nick) have been absolutely mowed out.

Any help or advice from any of you would be much appreciated.

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Nick
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Re: Beard P101 amplifier.

Post by Nick » Sun Feb 02, 2020 1:39 pm

I would guess it would be ok, but you would need to check the biasing. I would start up from a variac on maybe 75% voltage to make sure the bias is not going to be too far out.
Resistance isn't futile it's V / I.

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Re: Beard P101 amplifier.

Post by Chopsaw » Sun Feb 02, 2020 3:54 pm

Thanks Nick. We’re talking KT90s here? I’m assuming that the issue with the Beard is that it drives the output valves quite hard and it only worked reliably with the old GECs which are now rare and expensive!

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Re: Beard P101 amplifier.

Post by Nick » Sun Feb 02, 2020 6:13 pm

I don't know that amp, but the other beard I have seen looked as if the designer looked at the valve spec sheet and took the maximum values table as the typical operating conditions table but ignored the footnote that said only one of the maximums can be hit at once.
Resistance isn't futile it's V / I.

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Re: Beard P101 amplifier.

Post by Chopsaw » Sun Feb 02, 2020 6:58 pm

Thanks Nick that’s interesting. I think I need to get hold of a circuit diagram.

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pre65
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Re: Beard P101 amplifier.

Post by pre65 » Sun Feb 02, 2020 7:46 pm

Chopsaw wrote:
Sun Feb 02, 2020 6:58 pm
Thanks Nick that’s interesting. I think I need to get hold of a circuit diagram.
Good luck with that.
Life is what happens to you while you're busy making other plans. John Lennon

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Mike H
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Re: Beard P101 amplifier.

Post by Mike H » Sun Feb 02, 2020 8:05 pm

Nick wrote:
Sun Feb 02, 2020 6:13 pm
I don't know that amp, but the other beard I have seen looked as if the designer looked at the valve spec sheet and took the maximum values table as the typical operating conditions table but ignored the footnote that said only one of the maximums can be hit at once.
Blinking flip.

I would look at modifying it so that the 6550's become reliable. E.g. reduce the anode current or whatever.

I have destroyed a couple of full-wave rectifiers by flash-over, because I didn't look at the datasheet and the capacitance was too high, 50 -ish µF vs the 32 as abs. max. the sheet says (I think). Plus no limiting resistors. Just assumed it would work!
 
"Entrenched convictions cannot be changed by facts." – Dick Francis

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Nick
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Re: Beard P101 amplifier.

Post by Nick » Sun Feb 02, 2020 11:39 pm

I would look at modifying it so that the 6550's become reliable. E.g. reduce the anode current or whatever.
I am guessing the problem may be voltage rather than current, and reducing the current is likely to cause the voltage to increase.
Resistance isn't futile it's V / I.

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Re: Beard P101 amplifier.

Post by Chopsaw » Mon Feb 03, 2020 12:47 pm

Yes Mike, something a long those lines but someone else said the same as Nick that the voltage was too high and not easy to reduce.

Pre65, are you always this miserable?

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pre65
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Re: Beard P101 amplifier.

Post by pre65 » Mon Feb 03, 2020 1:02 pm

Chopsaw wrote:
Mon Feb 03, 2020 12:47 pm
Yes Mike, something a long those lines but someone else said the same as Nick that the voltage was too high and not easy to reduce.

Pre65, are you always this miserable?
No. :lol:

I've heard that Mr Beard does not like other people "messing" with his amps so deliberately makes info on them hard to get.

Things might be different nowadays ?

However, I hope you can get things sorted.
Life is what happens to you while you're busy making other plans. John Lennon

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Ali Tait
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Re: Beard P101 amplifier.

Post by Ali Tait » Mon Feb 03, 2020 1:10 pm

This may be it-

Image

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pre65
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Re: Beard P101 amplifier.

Post by pre65 » Mon Feb 03, 2020 2:26 pm

I found (no pun intended) where I read about circuit diagrams being difficult to obtain.(June 2006)

"Chris Found who has the rights to the Beard name is very reluctant to provide details...certainly no circuit diagrams."
Life is what happens to you while you're busy making other plans. John Lennon

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pre65
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Re: Beard P101 amplifier.

Post by pre65 » Mon Feb 03, 2020 2:30 pm

Ali Tait wrote:
Mon Feb 03, 2020 1:10 pm
This may be it-

Image
Quote "I asked Chris Found what should be in the amp and he said it should have
12AX7;12AT7;12BH7 in it.
But I haven't seen a circuit diagram, and think Bill Beard built them dependent on the O/P valves...mine are GE 6550 so I am fairly sure these are the originals. So I have to go on what he says...I've searched the net with no joy. Chris says it is basically a P100 with 8 O/P valves."
Life is what happens to you while you're busy making other plans. John Lennon

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Re: Beard P101 amplifier.

Post by Chopsaw » Mon Feb 03, 2020 8:58 pm

Thanks Ali, that’s a good start. Yes it may be that the P101 is just a P100 with an extra pair of output valves per side. There are a couple of ICs on the board too but I’ve no idea what they’re for. I’m no tech but I’m going to try and get it sorted somehow.

And thanks pre65. I don’t actually think Bill Beard will be too bothered now and is Chris Found still working? I thought he’d packed in but I could be wrong.

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Mike H
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Re: Beard P101 amplifier.

Post by Mike H » Thu Feb 06, 2020 8:39 pm

Nick wrote:
Sun Feb 02, 2020 11:39 pm
I would look at modifying it so that the 6550's become reliable. E.g. reduce the anode current or whatever.
I am guessing the problem may be voltage rather than current, and reducing the current is likely to cause the voltage to increase.
Chopsaw wrote:
Mon Feb 03, 2020 12:47 pm
Yes Mike, something a long those lines but someone else said the same as Nick that the voltage was too high and not easy to reduce.
Ah, see what you mean, yes.

Yes it does remind me in the KT88 datasheet (or one of them) there is an example o/p stage with large HT, 540V or summat.
 
"Entrenched convictions cannot be changed by facts." – Dick Francis

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