Decoupling DC heater supply between valves..benefit? - Page 2

regal · 27th May 2012, 07:29 AM

started with 200pf which helped but someone on here recommended 0.1uf and they work great, lowed measure thd (soundcard test) as I suppose the tube was wasting power oscillation in the mhz.

djgibson51 · 27th May 2012, 07:50 AM

Thanks, I'm using a lot of 6AK5 tubes (cos they were free) but they oscillate real easy. Never thought of the heater supply needing decoupling...

DF96 · 27th May 2012, 01:17 PM

The 6AK5 was designed for UHF amplification up to about 400MHz. It doesn't know that you only want it to work up to about 20kHz.

Failing to decouple the heater supply is unlikely to cause oscillation, except in some RF circuits, as the heater is mostly hidden inside the cathode, but it might spread the consequences of an oscillating valve. The solution is to stop the valve from oscillating by adding stoppers and ensuring that the cathode has a low inductance path to ground.

6J6 · 28th May 2012, 12:15 AM

Thanks for all the interesting replies, some good points to think about.

Seems that with DHT's it's a definate benefit, and perhaps oscillator tubes used in audio. I'm thinking of my favourite little cheap small signal tube the 6J6, which started life as a mixer/oscillator. It's indirect but I guess we shall see if it makes any difference.

For the sake of a cheap capacitor, why not

6J6 · 28th May 2012, 12:20 AM

Oh, and forgot to say djgibson51, 6AK5 / EF95 is a nice little pentode too. How does it compare to the EF86 in actual use for audio?

djgibson51 · 28th May 2012, 01:51 AM

I haven't any experience with the ef86, but love the flexibility of use, and clarity of sound of the 6AK5. Nor is it a "hungry" tube. See some of my 6AK5 adventures in the "100 buck amp" challenge

costis_n · 29th May 2012, 08:23 AM

I decouple with 2 (one per leg) 10n ceramic to chassis, at the first valve of the chain.
I have not tried decoupling every socket, but RF interference is shorted to ground once, so I am OK.

djgibson51 · 29th May 2012, 08:32 AM

Thanks costis.

DF96 · 29th May 2012, 09:58 AM

Quote:

Originally Posted by costis_n

RF interference is shorted to ground once, so I am OK.

You are only OK if any RF is at a fairly low frequency, or the heater chain is very short. Short RF here, and a quarter-wavelength away over there it has got stronger!

costis_n · 10:30 AM

Quote:

Originally Posted by DF96

You are only OK if any RF is at a fairly low frequency, or the heater chain is very short. Short RF here, and a quarter-wavelength away over there it has got stronger!

Well I got it off "Building Valve Amplifiers" and use it.

quarter-wavelength at these distances is around radar frequencies....

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
Transformer choice for DC heater supply?	dfro	Tubes / Valves	14	10th January 2011 07:46 AM
dc heater supply help	milen007	Tubes / Valves	17	21st February 2009 07:42 AM
Simple DC Heater Supply	d1camero	Tubes / Valves	9	19th October 2007 10:33 PM
regulated DC heater supply	jarthel	Tubes / Valves	30	29th May 2006 12:19 AM
Any benefit to DC heater on parallel supply rectifier (GZ34)?	leadbelly	Tubes / Valves	2	13th February 2006 11:00 AM

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


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

27th May 2012, 07:29 AM	#11
regal diyAudio Member Join Date: Jan 2004 Location: MD	started with 200pf which helped but someone on here recommended 0.1uf and they work great, lowed measure thd (soundcard test) as I suppose the tube was wasting power oscillation in the mhz.

27th May 2012, 07:50 AM	#12
djgibson51 diyAudio Member Join Date: May 2010 Location: Hawkes Bay	Thanks, I'm using a lot of 6AK5 tubes (cos they were free) but they oscillate real easy. Never thought of the heater supply needing decoupling...

27th May 2012, 01:17 PM	#13
DF96 diyAudio Member Join Date: May 2007	The 6AK5 was designed for UHF amplification up to about 400MHz. It doesn't know that you only want it to work up to about 20kHz. Failing to decouple the heater supply is unlikely to cause oscillation, except in some RF circuits, as the heater is mostly hidden inside the cathode, but it might spread the consequences of an oscillating valve. The solution is to stop the valve from oscillating by adding stoppers and ensuring that the cathode has a low inductance path to ground.

28th May 2012, 12:15 AM	#14
6J6 diyAudio Member Join Date: Feb 2012	Thanks for all the interesting replies, some good points to think about. Seems that with DHT's it's a definate benefit, and perhaps oscillator tubes used in audio. I'm thinking of my favourite little cheap small signal tube the 6J6, which started life as a mixer/oscillator. It's indirect but I guess we shall see if it makes any difference. For the sake of a cheap capacitor, why not

28th May 2012, 12:20 AM	#15
6J6 diyAudio Member Join Date: Feb 2012	Oh, and forgot to say djgibson51, 6AK5 / EF95 is a nice little pentode too. How does it compare to the EF86 in actual use for audio?

28th May 2012, 01:51 AM	#16
djgibson51 diyAudio Member Join Date: May 2010 Location: Hawkes Bay	I haven't any experience with the ef86, but love the flexibility of use, and clarity of sound of the 6AK5. Nor is it a "hungry" tube. See some of my 6AK5 adventures in the "100 buck amp" challenge

29th May 2012, 08:23 AM	#17
costis_n diyAudio Member Join Date: Aug 2008	I decouple with 2 (one per leg) 10n ceramic to chassis, at the first valve of the chain. I have not tried decoupling every socket, but RF interference is shorted to ground once, so I am OK.

29th May 2012, 08:32 AM	#18
djgibson51 diyAudio Member Join Date: May 2010 Location: Hawkes Bay	Thanks costis.