Thanks Tom! I'm not sure I'll try restuffing the tranny's, but you never know. :scratch2:

Yes but the grid resistors need to be 1-2 Megaohms not kiloohms. Once it is passing audio you may want to experiment with caps between .47 and .01, plate resistors between 8k and 15k, etc to optimize volume and tone. Audio amplifiers of that time were spectacularly inexact devices and could opperate deceptively normally with component values far from design or optimum.
What I gave you should get it to pass audio.
You will need a high impedance speaker/headphones or an audio matching transformer and a low impedance speaker... the plate resistance of a 01A is 11k ohms so you want an audio transformer with a primary impedance between 9k and 13k, and a secondary impedance that matches your speaker. Any transformer rated over 5W is probably over kill.

Thanks Tom, my mistake! I'm happy you caught that typo.

Fran

For posterity, here's the amended (final?) schematic with coupling caps and resistors bypassing the the two transformers:


http://videokarma.org/attachment.php...1&d=1566385424

I think I'm slowly becoming convinced that I should try this. I'll have to dig around my various parts stashes and see what I may have. :scratch2: I know I have some 70V PA speaker transformers that came with some full range 8" Jensens- would they do the job, do you think, or would the primary impedance be too low? I don't know how to determine those impedances between the windings.

I have some other old 40's-50's radios out in the barn, I can see if I can determine the values of their output trannys.

Sorry for all the probably stupid questions.

Hi Fran , Tom's method will work for you , I've done this many times and in fact I did the very same thing recently to a Temple brand TRF radio and it worked great . A couple of fine tuning tweaks here may be to use smaller capacitors for the coupling , I've usually found that much over .001 caused distortion , and with the Temple there was a bit of a buzz in the sound till I fed the plate resistor(the 10K resistor) with a small RF choke . The radio I did had only one bad interstage transformer and was an A/C powered unit , if you run your's from batteries you may not need the RF choke .

PS , there are no stupid questions here , we are mostly old men (:) Tom being the exception) who have spent a lifetime learning this stuff , and we are here specifically to help people learn what we spent all those years learning . Oh , and I love the "I is for him , E is for her" , my middle name is Francis and many people don't know the I or E spelling for male or female ;)

Thanks for the info! I'm an "old guy" myself, or at least closing in on that realm at 61. ;) Suffice it say, I've literally forgotten everything my dad taught me while helping him in my younger years (he was in the Army Radio Corps in WW2, Germany 1945 onward, then an electronics test engineer at General Dynamics and later R.F. Communications). We built tons of stuff before I went out (more or less) on my own at 17.

I just did a quick tutorial on the 70V line matching tx's and how to figure impedances between the primary (70V) and secondaries, and I think I can use one of the Jensens I have. The secondaries are labeled as (Watts) 4, 2, 1, 1/2, 1/4, and 1/8 into an "8 ohm speaker".

http://videokarma.org/attachment.php...1&d=1566396264

http://videokarma.org/attachment.php...1&d=1566396264

http://videokarma.org/attachment.php...1&d=1566396264

If my math is correct - following the innernut tutorials I watched (using the 70V primary and the 1/2 watt secondary):

W=E^2/R

W=5000/R

1/2=5000/R

R = 5000*W(1/2)

R(Impedance) = 10,000 ohms.

Gawd, I hope I didn't screw up the simple algebra. Been a reeeeaaaaalllllly long time. Am I on the right track, as far as the output of the final UX201A impedance?

Edit I see you are progressing on the pa transformer the way I would... I'm too tired to check the math, but it looks like your on the right track.

On the barn parts radios Google the audio output tube I'd number for each tube with the " tube datasheet" tacked onto the end of the search string...you should ring PDFs of pages from old RCA tube manuals and the like scan through the specs and look for plate resistance of the tube anything reasonably close to 11k should have a transformer that will work.....you can also order a new part from Hammond. Hammond makes new transformers for tube gear and probably has something that will work (try to get a part 5w or less or your paying for extra power your output tube will never be able to deliver to it).

Great! Thanks Tom, I appreciate the help.

Fran