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Welborne Labs 300B DRD (Tube Rectified) Manual
Welborne Labs 300B DRD (Tube Rectified) Manual
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Old 28th June 2018, 08:59 PM   #1
Ajay L is offline Ajay L
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Default Welborne Labs 300B DRD (Tube Rectified) Manual

Anybody have the Welborne Labs 300B DRD (Tube Rectified) manual?


I did try using Wayback Machine to try and retrieve it, as it had been available there for free download, but it was not archived.
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Old 28th June 2018, 09:32 PM   #2
6A3sUMMER is offline 6A3sUMMER  United States
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How about this:

Electra-Print.com 300B DRD Audio Tube Amplifier

Might be the same as the Welborne Labs version, might not.

Welborne Labs did use some of Electra Prints transformers, etc.

Last edited by 6A3sUMMER; 28th June 2018 at 09:35 PM.
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Old 28th June 2018, 10:33 PM   #3
6L6 is offline 6L6  United States
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Welborne Labs 300B DRD (Tube Rectified) Manual
I might have one but it would be buried deep away somewhere...

Are you looking for a specific piece of information? I build a few of them back in the day.
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Old 28th June 2018, 10:57 PM   #4
deafbykhorns is offline deafbykhorns  United States
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I have his book with schematics
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Old 29th June 2018, 12:48 AM   #5
RFBurns is offline RFBurns  United States
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I grabbed this off of the old Welborne site before it went offline. I think this is the one you were looking for.

RFBurns
Attached Files
File Type: pdf drd_300b_tr.pdf (572.1 KB, 190 views)
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Old 29th June 2018, 05:41 AM   #6
Ajay L is offline Ajay L
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Thank you so much RFBurns, this is exactly what I was after.

Quote:
Originally Posted by deafbykhorns View Post
I have his book with schematics
Any chance that this can be shared?

Quote:
Originally Posted by 6A3sUMMER View Post
How about this:
Electra-Print.com 300B DRD Audio Tube Amplifier

Might be the same as the Welborne Labs version, might not.

Welborne Labs did use some of Electra Prints transformers, etc.
Thanks 6A3sUMMER, I did come across this one, but I think the Welborne version operates at a lower voltage.

Quote:
Originally Posted by 6L6 View Post
I might have one but it would be buried deep away somewhere...

Are you looking for a specific piece of information? I build a few of them back in the day.
6L6, thanks for the offer to help, I may have a few questions down the line, just trying to get all my ducks in a row at this point.

By any chance would you happen to know what alternative transformers would be suitable for the Welborne version?
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Old 4th July 2018, 03:16 AM   #7
2wo is offline 2wo  United States
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I had the 45 version from Welborne and the iron used was Electra print...John
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Old 4th July 2018, 09:12 PM   #8
Ajay L is offline Ajay L
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Thank you, will check them out. Hopefully they're not too pricey...
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Old 13th July 2018, 01:00 AM   #9
deafbykhorns is offline deafbykhorns  United States
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Attached transformer info
Attached Images
File Type: jpg ED4091EB-6C02-45AC-8203-B1F2E01FB348.jpg (518.7 KB, 109 views)
File Type: jpg C8ED48B5-2C08-4F5F-95B3-ED9AF13B2CF6.jpg (491.4 KB, 108 views)
File Type: jpg B1EB9CE4-2BC4-4216-96F8-90447E8CAF24.jpg (499.7 KB, 108 views)
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Old 13th July 2018, 03:36 AM   #10
6A3sUMMER is offline 6A3sUMMER  United States
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Jay L and deafbykhorns,

The Welborne DRD amplifiers were DC coupled from driver tube plate to output tube grid. The DRD are 2 tube amplifiers. The B+ is medium to high, because the DRD design has lots of drop in the output tubes self bias resistor. That voltage across the self bias resistor is connected to the driver tube's plate choke. The output tube's self bias resistor's voltage drop has to be large enough to run the B+ required by the driver tube plate. The driver choke has a fairly low DCR, so the B+ drop is less than if a plate load resistor was used. There were 3 Welborne DRD amplifiers, a 45, a 2A3, and a 300B version.

The 2 stage Loftin White 2A3 amplifier (also DC coupled) has to have medium to large B+ because the output tube self bias has to run the driver tube. But the voltage needs to be even larger, because the driver tube plate load resistor has a larger drop than the plate load choke DCR of the DRD amps.

The power supply schematic in post #9 on the right is for the Welborne model Laurel amplifier, a 3 tube 300B amplifier. It is not a DRD amplifier power supply (look on the far lower right, you will see 'Laurel').

I met Ron Welborne at the early VSAC conferences in Silverdale Washington. I also met Jack Eliano of Electra-Print Audio (and have done business with him a number of times). They collaborated on the DRD amplifiers, but I do not know how many original and how many spinoff designs there may be.

I enjoyed the last VSAC Vacuum Tube State of the Art Conference in 2008 in Vancouver, WA. I presented a two part seminar, theory, and practical listening session then. VSAC 2008 ended a very nice conference series (sad to say).

I have a pair of the Electra-Print 3k to 2, 4, 8, 16 transformers, but I do not know if they were the exact ones used in the 300B DRD amp (they were made for 60 to 65 mA quiescent current).

Last edited by 6A3sUMMER; 13th July 2018 at 03:43 AM.
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