300B with interstage

summilux · 5th April 2011, 07:31 PM

Hi,

I'm looking around for a new amp project and I found this one. While I have a few scratch built amps under my belt, I am still learning when it comes to circuits. What is the purpose of the relays in the B- and C+ arms of the PS? Do I need them?

Thanks

Jonathan

Vinylsavor · 5th April 2011, 07:48 PM

Hi!

The relais in the B+ of the output stage will be triggered only when the bias voltage is there. This prevenst the B+ from being present to early in case bias is not settled yet and acts as a safety mechanism in case the bias fails, B+ will also be interrupted and thus avoid over current on the precious 300B.

For my taste the 417 is not a good choice as driver for the 300B since it will not have a lot of headroom. It will work however.

Best regards

Thomas

analog_sa · 08:43 PM

Most designs avoid this complication by using solid state rectification in the bias circuit. Tube bias is certainly much cooler.

Not liking relays much i would examine the possibility of using a directly heated diode for the bias instead.

summilux · 5th April 2011, 08:45 PM

Thomas,

I think I understand now. The switch on procedure for this amp would be: a) turn on main switch; b) wait for the heaters to come on, manually turn on the GZ37 relay which would then eventually automatically trigger the 24V relay in the 2nd EZ81.

Jonathan

Vinylsavor · 5th April 2011, 08:51 PM

Hi Johnathan,

no, it is much simpler: just turn on the main switch, the rest comes on automatically. With the mains switch on, both EZ81 start to heat up. Driver B+ and output stage bias come up. Once bias voltage exceeds a certain level, the relais for the outputstage B+ gets triggered

Thomas

5th April 2011, 07:48 PM	#2
Vinylsavor diyAudio Member Join Date: Feb 2002 Location: Lindau	Hi! The relais in the B+ of the output stage will be triggered only when the bias voltage is there. This prevenst the B+ from being present to early in case bias is not settled yet and acts as a safety mechanism in case the bias fails, B+ will also be interrupted and thus avoid over current on the precious 300B. For my taste the 417 is not a good choice as driver for the 300B since it will not have a lot of headroom. It will work however. Best regards Thomas __________________ http://vinylsavor.blogspot.com/

5th April 2011, 08:40 PM	#3
analog_sa diyAudio Member Join Date: Aug 2002 Location: Sofia	Most designs avoid this complication by using solid state rectification in the bias circuit. Tube bias is certainly much cooler. Not liking relays much i would examine the possibility of using a directly heated diode for the bias instead. Last edited by analog_sa; 5th April 2011 at 08:43 PM.

5th April 2011, 08:51 PM	#5
Vinylsavor diyAudio Member Join Date: Feb 2002 Location: Lindau	Hi Johnathan, no, it is much simpler: just turn on the main switch, the rest comes on automatically. With the mains switch on, both EZ81 start to heat up. Driver B+ and output stage bias come up. Once bias voltage exceeds a certain level, the relais for the outputstage B+ gets triggered Thomas __________________ http://vinylsavor.blogspot.com/

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
UTC A16 interstage 300B	neskor	Tubes / Valves	2	30th March 2011 04:02 PM
SJS SE 300B with Interstage Transformer Mk2	DVDHack	Tubes / Valves	29	20th August 2008 11:52 AM
Anyone used interstage transformers for a 300B?	duderduderini	Tubes / Valves	20	11th August 2008 01:31 PM
417A-300B Plate Choke or Interstage Coupled?	sgerus	Tubes / Valves	21	14th January 2007 12:45 AM
300b Push Pull Interstage Tsf	brsanko	Tubes / Valves	7	2nd March 2005 01:46 PM

5th April 2011, 08:45 PM	#4
summilux diyAudio Member Join Date: Jul 2004 Location: ottawa	Thomas, I think I understand now. The switch on procedure for this amp would be: a) turn on main switch; b) wait for the heaters to come on, manually turn on the GZ37 relay which would then eventually automatically trigger the 24V relay in the 2nd EZ81. Jonathan

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read