We417+300b

China_Vincent · 21st December 2007, 05:13 PM

HI:
I want do a the 300 Bs of structure like this, which friend have already done?
Thanks!
China_vincent

dave slagle · 21st December 2007, 05:50 PM

If you build it as drawn, try bypassing the 3K3 resistor on the grid of the 300B wiht a clip lead and see how the sound changes. It is not needed for proper circuit operation.

dave

kevinkr · 21st December 2007, 06:20 PM

Quote:

Originally posted by dave slagle
If you build it as drawn, try bypassing the 3K3 resistor on the grid of the 300B wiht a clip lead and see how the sound changes. It is not needed for proper circuit operation.

dave

I generally use 1K resistors here, and that is as assurance against VHF oscillations which do occasionally occur even with 300B dht depending on layout. The noise contribution of that resistor is miniscule in relation to the signal levels present at that point.

Of more concern is the fact that the 417A needs to be handled very carefully when swinging these kinds of plate voltages as you will be swinging the grid over more or less its entire linear operating range and then some. I would use a 1:2 or 1:2.25 step up here - say 10K:40K/50K or similar. (Note that the driving source Z seen by the 300B with the proposed changes will be less than 10K with 1:2, less than 12K with 1:2.25 so HF BW will be ok.)

I have designed and built choke loaded 417A/5842 to drive 71A - works really well, and sounds great. I've no doubt with the right IT you will achieve excellent results. I run the 417A at 15 - 20mA with 150V on the plate. (Approximately -1 to -1.2V fixed bias on the grid, varies a lot due to variations in GM from tube to tube.)

zigzagflux · 21st December 2007, 06:43 PM

The 100V rating of the cathode bypass cap seems a little marginal to me, especially if you're choosing an electrolytic. Lower ESR is obtained with higher voltage rated caps (which is easy to find in 220 uF).

China_Vincent · 8th May 2008, 02:40 PM

WE417-300B

China_Vincent · 8th May 2008, 02:41 PM

WE417-300B

oldeurope · 8th May 2008, 03:05 PM

Looks very good.

Do you have an inside view?

Kind regards,
Darius

coresta · 8th May 2008, 07:52 PM

Darius, would you have a pair of RL12T15 sockets ?

tube-lover · 8th May 2008, 08:34 PM

hi oldeurope,

will U considerate this circuit?

417a & 437a was close.

thx

thomas

jlsem · 8th September 2008, 05:35 AM

Does anyone know what happened to Thomas of Diyaudio.hk (tube-lover)? He ripped me off to the tune of $800 on eBay for one of his amplifier kits.

John

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21st December 2007, 05:50 PM	#2
dave slagle diyAudio Member Join Date: Mar 2003 Location: NYC	If you build it as drawn, try bypassing the 3K3 resistor on the grid of the 300B wiht a clip lead and see how the sound changes. It is not needed for proper circuit operation. dave

21st December 2007, 06:43 PM	#4
zigzagflux diyAudio Member Join Date: Oct 2006	The 100V rating of the cathode bypass cap seems a little marginal to me, especially if you're choosing an electrolytic. Lower ESR is obtained with higher voltage rated caps (which is easy to find in 220 uF).

8th May 2008, 03:05 PM	#7
oldeurope diyAudio Member Join Date: Mar 2008	Looks very good. Do you have an inside view? Kind regards, Darius

8th May 2008, 07:52 PM	#8
coresta diyAudio Member Join Date: Mar 2005 Location: Paris	Darius, would you have a pair of RL12T15 sockets ?

8th September 2008, 05:35 AM	#10
jlsem diyAudio Member Join Date: Jun 2003 Location: Dallas,TX	Does anyone know what happened to Thomas of Diyaudio.hk (tube-lover)? He ripped me off to the tune of $800 on eBay for one of his amplifier kits. John

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