Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Alien on July 21, 2010, 11:46:04 am

Title: OT impedence question
Post by: Alien on July 21, 2010, 11:46:04 am

I've built one amp so far, a 1959-alike using a pair of EL84's for about 15W.  Finding a suitable OT was simple, as the datasheets told me what impedence I needed.

I've now come by a few Russian sub-mini pentodes that I'd like to use, and have no idea what parameters relate to the impedence.  I've tried looking at the EL84 specs to see if I could relate one to another, but nothing seems to match up.

Can anyone help with some info on how tube specs relate to OT impedence please?

Thanks

Andy

Title: Re: OT impedence question
Post by: tubeswell on July 21, 2010, 02:42:04 pm

Hi Andy - which russkie tubes would those be?

Title: Re: OT impedence question
Post by: Alien on July 21, 2010, 05:29:05 pm

Hi Tubeswell.  They're 6Ж1Б-В (6Z1B-V).  I have been told they were used as audio and RF power tubes.

I'm having to translate the datasheets (mostly one word at a time) using convertcyrillic.com, as I can't find any information on these tubes anywhere.

Any help gratefully received

Andy

Title: Re: OT impedence question
Post by: Dave on July 21, 2010, 05:45:56 pm

Here you go. Everything you need is right here.

http://www.diystompboxes.com/smfforum/index.php?PHPSESSID=a4aecb910c81eefdfb1fd58c19813c82&topic=81848.0

Title: Re: OT impedence question
Post by: FYL on July 21, 2010, 05:47:25 pm

Quote

They're 6Ж1Б-В (6Z1B-V).  I have been told they were used as audio and RF power tubes.

They are listed as a Russian version of the 5702.

http://www.next-tube.com/Data/USA-RUS.pdf => page 5

Tung Sol datasheet:
http://frank.pocnet.net/sheets/127/5/5702WA.pdf

Plate resistance is listed at 340K...

Title: Re: OT impedence question
Post by: HotBluePlates on July 21, 2010, 07:14:35 pm

These are listed as a sharp-cutoff pentode, which is a tip-off that this is a preamp tube. Are you trying to use it in a preamp or as an output tube?

If output tube, you're best off pretending it is the same as a 6AU6, and copy PRR's 1/3w amp, which uses a reverb transformer as a SE output transformer.

There is a test condition listed on the data sheet of 120v on the plate and 0.9w of dissipation. 0.9w / 120v = 7.5mA, and 120v/7.5mA = 16k ohms. Rough first guess, use a 16k load. Old tube books say that triodes are loaded for max power with a load of twice the plate resistance, which would be 32k in this case (that's "apparent plate resistance, not actual). I think a reverb transformer is something like 22-24k, so it's close enough. You won't get max power, but if you're using this tube as an output tube then max power is obviously not a priority. Expect maybe 1/4-1/3w output.

Title: Re: OT impedence question
Post by: tubeswell on July 21, 2010, 07:24:59 pm

Quote from: Alien on July 21, 2010, 05:29:05 pm

Hi Tubeswell.  They're 6Ж1Б-В (6Z1B-V). 
Any help gratefully received

Hi Andy looks like the others have got it covered. incidentally is this the same tube?

http://www.russiantubes.com/prop.php?t=12&p=115

Title: Re: OT impedence question
Post by: Alien on July 22, 2010, 05:26:29 am

Quote from: tubeswell on July 21, 2010, 07:24:59 pm

Hi Andy looks like the others have got it covered. incidentally is this the same tube?

http://www.russiantubes.com/prop.php?t=12&p=115

That looks like the ones I've got.

Thanks for all the help guys, that's a great starting point.  I'll keep you all posted on the build if it looks like a goer.

Andy