vinyvamos
Well-known member
Has anyone yet tried the Lundahl LL1635 in a BA-6A build? It would be great to get proof of an alternative to the Sowter 
Ba6a interstage
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vinyvamos
Well-known member
Correct me if I'm wrong, but from what I understand from this thread no THD tests were performed with the various interstage options, and no inductance or DC-R measurements were done on the original BA6A interstage trafo that Lassoharp and EMRR were testing with. The latter is crucial surely for replicating this iron. Although we have a confirmation that frequency response is ok with various trafos, it seems like the picture is still not fully clear. Phase distortion comes in before a reduction in LF response is measured, and this would be caused by lack of L in traofs. Is there still a BA6A interstage available for testing? Surely if the original BA6A interstage has say 500H like the 86 interstage has and we put in a sowter with 120H, there will be differences. Also, the physical size of the original RCA iron seems far bigger than what Sowter are offering. The Sowter interstage is listed as a type J with 43x36mm laminations. The RCA cans are 78mm dia x 100mm tall! Now either RCA were trying to make their limiter look beefy and placed small trafos in big cans, or the original cores are much bigger than Sowter. Does this mean anything even? Possibly not, but certainly if RCA had much higher inductance then a larger core would allow for the miles of wire, plus a very decent headroom...
"Now either RCA were trying to make their limiter look beefy and placed small trafos in big cans, or the original cores are much bigger than Sowter."
Why on earth would this even remotely be a consideration for RCA in the 1940s? From the get-go the move was toward smaller systems. The pressure was on making everything more compact. (and presumably less costly). Shielding made the cans bigger in general and no modern trafo maker that I have seen offers the level of shielding that was standard back then.
Why on earth would this even remotely be a consideration for RCA in the 1940s? From the get-go the move was toward smaller systems. The pressure was on making everything more compact. (and presumably less costly). Shielding made the cans bigger in general and no modern trafo maker that I have seen offers the level of shielding that was standard back then.
vinyvamos
Well-known member
OK point taken. So are we talking half an inch of shielding here? I think the tests that yourself and Doug did were extremely helpful to the cause here, but damn damn I wish you had tested the L & DC-R of the original BA6A interstage
Read it again. We never had an original.OK point taken. So are we talking half an inch of shielding here? I think the tests that yourself and Doug did were extremely helpful to the cause here, but damn damn I wish you had tested the L & DC-R of the original BA6A interstage
vinyvamos
Well-known member
Oops, my bad. I had misread one of Lassoharps replies and took it that you had an original
Bumping an old thread but any update on the availability of these so tests could be performed?
guessing not, being in Russia.....
Rob Flinn
Well-known member
I just ordered one of these to try out https://www.mouser.co.uk/ProductDetail/Hammond-Manufacturing/835?qs=1ADZffG2MqvTeKKesWPBlQ==
It took a few months to come through because I believe it's a special order.
It took a few months to come through because I believe it's a special order.
Hi Rob,
Nice, I've been thinking about that one, too but am only slowly gathering parts now as I'm unfortunately in the middle of a move...
I've seen a lot of your posts over the years, I look forward to your review!
Thanks,
Chris
P.S. Not to hijack this thread but what're your thoughts on the Hammond 812 for the control amp input for a Fairchild 6x0 build? I asked in that thread but got no input (bad pun...). If you have any thoughts, you can PM to keep this thread clean/on-topic.
Nice, I've been thinking about that one, too but am only slowly gathering parts now as I'm unfortunately in the middle of a move...
I've seen a lot of your posts over the years, I look forward to your review!
Thanks,
Chris
P.S. Not to hijack this thread but what're your thoughts on the Hammond 812 for the control amp input for a Fairchild 6x0 build? I asked in that thread but got no input (bad pun...). If you have any thoughts, you can PM to keep this thread clean/on-topic.
Rob Flinn
Well-known member
Don't expect any opinions anytime soon. I'm away for the rest of the month & have work backed when I return.
No idea about the 812.
Rob Flinn
Well-known member
Got a bit further with this recently (unfortunately due to lack of paid work).
For reference the Hammond 835 has d.c resistances of
Pri 1 866R
Pri 2 1050R
Sec 1 930R
Sec 2 956R
Not at a stage to run audio yet as I'm waiting for some parts.
It will work just fine. Been there, done that. Not sure what you are looking to confirm or deny. That info was present for the tests Doug and I ran some years ago that is documented in the group. But, sometimes there's no need to mention things directly, and good reasons for doing so.
Rob Flinn
Well-known member
I'm not looking to confirm or deny anything. I didn't see any specific info about this transformer from you or Doug which is why I added it. I don't have an inductance meter, therefore can't add any figures in that respect. Fazeka just asked for info. Unfortunately since I bought this transformer new from Mouser earlier this year as a special order they have now discontinued it from their catalogue, so I'm not sure if Hammond even still manufacture it.
"But, sometimes there's no need to mention things directly, and good reasons for doing so." It's there, to be inferred from the commentary. Hammond still manufactures it, so it won't be unobtanium. Hawk has them
https://www.hawkusa.com/search-quer...rohs_compliant=All&items_per_page=10&offset=0
Hammond 835, DCR's on their sheet, inductances measured range 900-1100H.
850Q, 1700ish H.
https://groupdiy.com/threads/rca-ba-6a-problem-solved.69476/page-4#post-901122
850Q, 1700ish H.
https://groupdiy.com/threads/rca-ba-6a-problem-solved.69476/page-4#post-901122
Mickeyvee
Member
Hi there guys i have a drip rca ba6a comp which eas bought by me quite cheap it did not have the right meter in it do the original tech who went over it a very experienced valve tech here in Australia he is 80 and this big bugger is too heavy for him to work on even tho he completed the resto beautifully and callibrated the tech meter to work since then i bought a new nos original ba6a meter i have given it to another tech to put it in he has but wants to know hss anyone got info on how to callibrate it even access to a manual or anything would be fab this forum is great i just had tubtec sort out an issue with the. Vortexion 3/ppm meter to great avail !!! Thanx
If you have an original then it should just go in, but if you want to check the calibration, then I would do it like this:-
A VU meter is designed to read O VU when in series with a 3.6k resistor, when 1.228V rms is across them both. You would need something like a signal generator with a 600 ohm output and set at say 400Hz. You can measure the voltage with a half decent DVM, there is no need to get picky about it, 1.23V would be fine. For more details read https://en.wikipedia.org/wiki/VU_meter
best
DaveP
A VU meter is designed to read O VU when in series with a 3.6k resistor, when 1.228V rms is across them both. You would need something like a signal generator with a 600 ohm output and set at say 400Hz. You can measure the voltage with a half decent DVM, there is no need to get picky about it, 1.23V would be fine. For more details read https://en.wikipedia.org/wiki/VU_meter
best
DaveP
And here's the manual:
https://www.dropbox.com/scl/fi/fftc...-516.pdf?rlkey=591y4lmrjwuayeomp34741eik&dl=0
https://www.dropbox.com/scl/fi/fftc...-516.pdf?rlkey=591y4lmrjwuayeomp34741eik&dl=0
