Surprising bread board test.

Posted by twystd (A) on March 2, 2015 at 19:47:02

Wanted to post some interesting results on an amp project I've been working on. It's an integrated parafeed 6p36s amp with a 6e6p-dr driver stage, both operating in triode mode. Driver stage: diode bias, CCS plate load (K&K audio), shunt regulated (K&K Audio), cap coupled to 6p36s parafeed power stage: 50h plate choke (one electron), 3K nickle parafeed OPT (Magnequest), 12uf KBG parafeed cap. Power supply: damper diodes, critical inductance LCLC filter sections.

I have a bud who is an EE, and he brought by his oscilloscope, and signal generator. We first tested it with a CCS on the cathode, and 150uf cathode bypass cap. Power output was 8.5 watts before clipping, bandwidth was 10hz-23khz before we could detect any drop off. We next replaced the CCS on the cathode with a 500 ohm cathode resistor, it measured the same, but we thought it sounded a little better. Next we tried it with an unbypassed cathode resistor. I thought we might get away with it, since it is using the kind of parafeed that returns what would normally be the ground side of the OPT primary, to the top of the cathode resistor. It measured 7.5 watts output before clipping, bandwidth was a little down on the low side, perfectly flat to 30hz rather than 10hz. Since my speakers start to fall off like a rock below 30hz, I see no problem with that. The upper bandwidth was the same, at 23khz, before there was any measurable loss. We thought the unbypassed cathode resistor really sounded good, and I can certainly live with 7.5 watts (I was expecting 6). I was also happy to see it had only .6mv of hum on the outputs.

The surprising thing was how efficient the 6p36s was, it was dissipating 20 watts, and putting out 8.5! I'm thinking that big old 50h choke, running at 75ma had something to do with that too. We were also surprised how little power we lost, with the unbypassed cathode resistor. I know some may think that 20 watts dissipation is a lot for a 6p36s, but I've been lurking on the Russian forums, and that is where most of them are running (usually between 18 and 22 watts). I'm sure that returning the parafeed cap to the top of the cathode contributed to just losing 1 watt, with the unbypassed cathode resistor. I think that's a small price to pay to not have that large cathode bypass cap. So far, I'm a happy camper, when I finish the amp I'll post.

BTW according to the plate curves, the 6p36s, at my operating points, has an Rp of about 500 ohms, so the 3k OPT should have plenty of impedance. It is also interesting that according to the plate curves, the 6p36s in triode mode, is more linear than a 2A3.

twystd

This post is made possible by the generous support of people like you and our sponsors:

Topic - Surprising bread board test. - twystd 19:47:02 03/02/15 (2)

RE: Surprising bread board test. - Caucasian Blackplate 20:26:20 03/02/15 (1)

RE: Surprising bread board test. - twystd 20:38:31 03/02/15 (0)

FAQ

Post a Message!

Forgot Password?

Moniker (Username):
Password (Optional):
	Remember my Moniker & Password (What's this?) Eat Me
E-Mail (Optional):
Subject:

Message:	(Posts are subject to Content Rules)

Optional Link URL:
Optional Link Title:
Optional Image URL:
Upload Image:
E-mail Replies:	Automagically notify you when someone responds.

To view your new posting or follow-up, click on the RELOAD or REFRESH button on your browser.