Can anyone explain what part values are between pins 1 and 3 in the attached illustration and what their function is? Thanks in advance...
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question about express layout
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question about express layout
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Re: question about express layout
They're 3x IN4007 diodes in series.
I think they're there to prevent the plate going negative WRT cathode. They're basically a safety feature and have no effect on tone.
I think they're there to prevent the plate going negative WRT cathode. They're basically a safety feature and have no effect on tone.
Re: question about express layout
I can tell you for sure that they're diodes. They're unique as far as I've seen to the Kelly 90 schematic. They are connected between the cathode and plate of the 6l6s.
According to Allynmey they protect your OT from transients and in case of tube failure. I think the idea is the breakdown voltage is such that if there were a really bad voltage spike the diodes would short the circuit.
This thread has a little info:
"https://tubeamparchive.com/viewtopic.ph ... ly++diodes
I think it would also protect the OT in the event the amp got started up without a load on the output.
Someone who actually understands how this works, please correct/clarify my info.
According to Allynmey they protect your OT from transients and in case of tube failure. I think the idea is the breakdown voltage is such that if there were a really bad voltage spike the diodes would short the circuit.
This thread has a little info:
"https://tubeamparchive.com/viewtopic.ph ... ly++diodes
I think it would also protect the OT in the event the amp got started up without a load on the output.
Someone who actually understands how this works, please correct/clarify my info.
Re: question about express layout
Ken used them in a lot of his amps. They are documented in "The Trainwreck pages" in gerald webers books. They are protection for the OT if a tube shorts and for transient spikes of current.
Allynmey
Allynmey
Re: question about express layout
Are those the same TWreck pages in the files section?
Re: question about express layout
The diodes are to protect both the tubes and the transformer against flyback transients.
A 1N4007 has a reverse breakdown voltage of something like 1000V, after which it will conduct in both directions. In the Express example, with three connected in series between the plate and ground, they won't conduct until there is a voltage of above 3000V at the plate, and this will then be dumped to ground rather than into the output tube.
It also prevents the inductive nature of the transformer from attempting to raise the voltage higher in order to maintain the magnetic flux (as inductors do), which would ultimately result in arcing across the windings and permanent damage to the transformer.
A 1N4007 has a reverse breakdown voltage of something like 1000V, after which it will conduct in both directions. In the Express example, with three connected in series between the plate and ground, they won't conduct until there is a voltage of above 3000V at the plate, and this will then be dumped to ground rather than into the output tube.
It also prevents the inductive nature of the transformer from attempting to raise the voltage higher in order to maintain the magnetic flux (as inductors do), which would ultimately result in arcing across the windings and permanent damage to the transformer.
Re: question about express layout
Do the diodes provide the same protection in a cathode bias amp?
Rich Gordon
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"The takers get the honey, the givers get the blues." --Robin Trower
www.myspace.com/bigboyamplifiers
"The takers get the honey, the givers get the blues." --Robin Trower
Re: question about express layout
They'll work just the same in a cathode-biased amp.
I use them routinely as a safety measure in all new builds as half a dozen 1N4007s cost significantly less than an OT or a pair of NOS tubes.
I use them routinely as a safety measure in all new builds as half a dozen 1N4007s cost significantly less than an OT or a pair of NOS tubes.
Re: question about express layout
No, it's in the builders interview section at the back of Webers book, "Tube Guitar Amplifier Essentials".benoit wrote:Are those the same TWreck pages in the files section?
It is still in print, so go get a copy! Or do it on the cheap; Borders sometimes has them in stock. Buy a cup of coffee and read
That interview alone is worth the price of the book, plus it's a pretty good book.