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THE BIG ONES . . . RCA MI-9359 resurrection begins . . .
- Thread starter markus
- Start date
markus
Master Procrastinator
9358
so close . . . .no worries - tracing the circuit lets me get intimate with the amp :thmbsp:
markus
Master Procrastinator
making progress . . . .
successfully bypassed the input transformer on both amps (just with test leads for now), and hum is MUCH reduced . . . . the grids of the 6SN7 tube are paralleled, so I merey clipped my lead to this connection . . . would it help to remove the input transformer connection altogether from the circuit? (i have yet to snip that lead . . . )
I noticed there are two small electrolytic caps in the PS circuit - I'll be adding those to the shopping list in addition to the signal caps I need . . . .
I've brought each amp up to full voltage (110VAC) and on one of the amps the music volume fades in and out . . . I'm guessing out of spec resistors in a bias circuit? I'm not gonna mess around . . . just gonna order all new resistors so I don't need to worry about it.
some measurements thus far:
300 VDC on the 2A3 plates (to ground)
450 VDC on the 809 plates (to ground) (YIKES!)
130 - 140 VDC on the 6SL7 plates (to ground)
my 809's are definitely not matched . . . all from different sources - a couple new, some came with the amp . . . could I do that trick where I bias them individually? maybe even with some large(ish) variable resistors ? ideally I'd like to bias the tubes on the 'gentle' side so I don't burn through 2A3's and 809's as RCA intended
back to tracing the circuit on paper to help me understand what the hell these monsters are up to . . . :thmbsp:
successfully bypassed the input transformer on both amps (just with test leads for now), and hum is MUCH reduced . . . . the grids of the 6SN7 tube are paralleled, so I merey clipped my lead to this connection . . . would it help to remove the input transformer connection altogether from the circuit? (i have yet to snip that lead . . . )
I noticed there are two small electrolytic caps in the PS circuit - I'll be adding those to the shopping list in addition to the signal caps I need . . . .
I've brought each amp up to full voltage (110VAC) and on one of the amps the music volume fades in and out . . . I'm guessing out of spec resistors in a bias circuit? I'm not gonna mess around . . . just gonna order all new resistors so I don't need to worry about it.
some measurements thus far:
300 VDC on the 2A3 plates (to ground)
450 VDC on the 809 plates (to ground) (YIKES!)
130 - 140 VDC on the 6SL7 plates (to ground)
my 809's are definitely not matched . . . all from different sources - a couple new, some came with the amp . . . could I do that trick where I bias them individually? maybe even with some large(ish) variable resistors ? ideally I'd like to bias the tubes on the 'gentle' side so I don't burn through 2A3's and 809's as RCA intended
back to tracing the circuit on paper to help me understand what the hell these monsters are up to . . . :thmbsp:
markus
Master Procrastinator
another question . . . the 2A3 plates appear to be coupled to the 809 grids via a 620 Ohm resistor, in series with a .0035 / 1000V cap . . .
should I just stick with these values ? my thought is to get everything to a baseline of what it was when new, and then go from there, since there is zero info on these guys online . . .
should I just stick with these values ? my thought is to get everything to a baseline of what it was when new, and then go from there, since there is zero info on these guys online . . .
Scuzzer
Fixed Bias
Here's what I would do.
1. Trace the circuit and draw up a really solid schematic.
2. Replace components with the same type and value of resistor or cap.
3. Test the heck out of it to see what it can do stock.
4. Solicit advice for upgrades to remedy any deficiencies found in step 3.
5. Decide if I wanted to actually do those upgrades or try and sell the pair (with stock values) to some guy with tons of cash in the Far East.
I've been envious of your project ever since you posted this thread. Big old theater amps are so cool even if they're a bit impractical.
edit: I'm looking forward to seeing the schematic once you get it all prettied up. Like you said, there is no info online about these.
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markus
Master Procrastinator
thanks Scuzzer - excellent advice :thmbsp:
although these are right up there with my JBL C36 - they can pry them from my cold dead hands !! it would be fitting to find a pair of RCA theater speakers (horns and woofers) and put these monsters to work . . . not that I have a spare $3K kicking around, but you know . . . .
just measured the 2a3 grid resistors . . both have drifted and are next to be replaced . . . 2A3 bias resistors are next me thinks . . I'm betting they are the biggest culprit . . .
although these are right up there with my JBL C36 - they can pry them from my cold dead hands !! it would be fitting to find a pair of RCA theater speakers (horns and woofers) and put these monsters to work . . . not that I have a spare $3K kicking around, but you know . . . .
just measured the 2a3 grid resistors . . both have drifted and are next to be replaced . . . 2A3 bias resistors are next me thinks . . I'm betting they are the biggest culprit . . .
Phototone
Super Member
thanks Scuzzer - excellent advice :thmbsp:
although these are right up there with my JBL C36 - they can pry them from my cold dead hands !! it would be fitting to find a pair of RCA theater speakers (horns and woofers) and put these monsters to work . . . not that I have a spare $3K kicking around, but you know . . . .
just measured the 2a3 grid resistors . . both have drifted and are next to be replaced . . . 2A3 bias resistors are next me thinks . . I'm betting they are the biggest culprit . . .
You do realize these were for Drive-In Theater use, powering perhaps hundreds of little 4" in-car speakers through a 70v PA type distribution arrangement. It would be extreme overkill for a horn-loaded large speaker system.
markus
Master Procrastinator
hmm . . . I'm a bone head - check the simple sh*t first guys . . and look before you cut !
made two mistakes . . .
what I thought was the incoming wire from the input tranny to the 6SL7 was actually part of the feedback loop (cause of the weird oscillation / volume fluctuation)
my 'test' RCA cable going into the amp was unshielded
resoldered the cut connection, used a shielded rca cable and POOF . . .
this monster is SINGING . . . still *very* slight hum, which I blame on the unshielded jumper I still have to use for the long run from cd player to amp, and those 2 60 year old electrolytic caps that will be replaced. I threw some caps in parallel to take care of the coupling caps . . .still want to do the 'forever' recap with better ones.
BUT . . . I have one pushing a Original Large Advent and it's thumping :thmbsp: never seen a tube amp overpower an OLA before!
I'll add some pictures soon . . . the little test meter / VU meter on this 1946 RCA monster hasn't danced like this in decades I'm sure
made two mistakes . . .
what I thought was the incoming wire from the input tranny to the 6SL7 was actually part of the feedback loop (cause of the weird oscillation / volume fluctuation)
my 'test' RCA cable going into the amp was unshielded
resoldered the cut connection, used a shielded rca cable and POOF . . .
this monster is SINGING . . . still *very* slight hum, which I blame on the unshielded jumper I still have to use for the long run from cd player to amp, and those 2 60 year old electrolytic caps that will be replaced. I threw some caps in parallel to take care of the coupling caps . . .still want to do the 'forever' recap with better ones.
BUT . . . I have one pushing a Original Large Advent and it's thumping :thmbsp: never seen a tube amp overpower an OLA before!
I'll add some pictures soon . . . the little test meter / VU meter on this 1946 RCA monster hasn't danced like this in decades I'm sure
markus
Master Procrastinator
yes . . . I understand that - the output transformer has multiple speaker impedance taps (at least that's how I'm understanding the labeling) : 250, 60, 30, 15, 7.5, 3.75, 'S', and then 'incoming' taps for the output tubes
the 250 tap is connected to a terminal marked 'HI' (guessing high impedance?)
the 3.75 tap is connected to a terminal marked 'LOW' (low impedence?)
I do know this was connected also to a monitor speaker, which I also have (speaker is rated at 2 ohms, and was connected to the 'LOW' terminal originally)
there's a terminal marked 'C' which I'm assuming is common ground . . .
so, I've merely got the Advent connected to the low & C terminals. playing nicely
I just like the idea of running these with period correct speakers, that's all. I know the old theater setups are ridiculously efficient.
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markus
Master Procrastinator
more info . . .
http://www.film-tech.com/warehouse/manuals/RCAPG250251INSTALL.pdf
http://www.film-tech.com/warehouse/manuals/RCAPG250251OPER.pdf
the operating manual gives the only spec's I've been able to find . . .
http://www.film-tech.com/warehouse/manuals/RCAPG250251INSTALL.pdf
http://www.film-tech.com/warehouse/manuals/RCAPG250251OPER.pdf
the operating manual gives the only spec's I've been able to find . . .
Scuzzer
Fixed Bias
Awesome documentation but unless I missed it no schematic. It's like a complete DIY manual on how to build a drive-in theater.
That's the whole point, isn't it?
That's the whole point, isn't it?
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fizzgig
Well-Known Member
funny, this is what I got back from my friend at Film-Tech...if you want me to I will remind him for a follow up in a week.
---------------------------
from Jxxx Sxxx jsxxxx@film-tech.com
sender-time Sent at 5:22 PM (GMT-05:00). Current time there: 5:24 PM. ✆
to Jeff <jxxxxxx@gmail.com>
date Tue, Oct 25, 2011 at 5:22 PM
subject RE: RCA MI-9359
Important mainly because of the people in the conversation.
hide details 5:22 PM (1 minute ago)
Anything that Brad would have is on his website. Oddly enough, I am going to a drive in owners convention next week and I will try to ask about it there. Try to remind me in about a week (I am in Miami now at a trade show).
From: Jxxxxxxxxxx [mailto:jxxxxxxxxxxx@gmail.com]
Sent: Tuesday, October 25, 2011 4:40 PM
To: Jxxxxx Sxxxxx
Subject: RCA MI-9359
There is a guy on Audiokarma looking for schematics for a couple RCA MI-3659 drive in theater tube amps. they've located the operating manuals on the film-tech website, but no schematics. Do you know if you or brad would have them?
here is a link to the thread:
http://www.audiokarma.org/forums/showthread.php?t=399162
---------------------------
from Jxxx Sxxx jsxxxx@film-tech.com
sender-time Sent at 5:22 PM (GMT-05:00). Current time there: 5:24 PM. ✆
to Jeff <jxxxxxx@gmail.com>
date Tue, Oct 25, 2011 at 5:22 PM
subject RE: RCA MI-9359
Important mainly because of the people in the conversation.
hide details 5:22 PM (1 minute ago)
Anything that Brad would have is on his website. Oddly enough, I am going to a drive in owners convention next week and I will try to ask about it there. Try to remind me in about a week (I am in Miami now at a trade show).
From: Jxxxxxxxxxx [mailto:jxxxxxxxxxxx@gmail.com]
Sent: Tuesday, October 25, 2011 4:40 PM
To: Jxxxxx Sxxxxx
Subject: RCA MI-9359
There is a guy on Audiokarma looking for schematics for a couple RCA MI-3659 drive in theater tube amps. they've located the operating manuals on the film-tech website, but no schematics. Do you know if you or brad would have them?
here is a link to the thread:
http://www.audiokarma.org/forums/showthread.php?t=399162
markus
Master Procrastinator
markus
Master Procrastinator
some more pictures . . .
here's some internal shots of the work in progress. check out the closeup of the dental tool - this appears to be oozing (past / present - not sure) from one of the oil caps :scratch2: I'm guessing that bastard is leaking . . . . can someone confirm ?
it's not a huge deal - I have a stash of these big 1000V oil caps . . .
I also included a shot of the terminal strips to see if anyone can offer feedback. in order, from top to bottom, the connections are: AC (hot & neutral), Test, HI, LOW, C (common Ground?), 6.3 (+ & -)
back to tracing the circuit . . . . :thmbsp:
here's some internal shots of the work in progress. check out the closeup of the dental tool - this appears to be oozing (past / present - not sure) from one of the oil caps :scratch2: I'm guessing that bastard is leaking . . . . can someone confirm ?
it's not a huge deal - I have a stash of these big 1000V oil caps . . .
I also included a shot of the terminal strips to see if anyone can offer feedback. in order, from top to bottom, the connections are: AC (hot & neutral), Test, HI, LOW, C (common Ground?), 6.3 (+ & -)
back to tracing the circuit . . . . :thmbsp:
Attachments
markus
Master Procrastinator
Ah ha !!!!
so I've been organizing the basement and garage, and guess what I found ? 3 more 5R4 rectifiers, and three more 809's (2 of which will need to be soldered into the plate cap, but I'll take it)
NOW . . . if I can just find a cheapy pair of 2A3's, I can get these monsters going in STEREO !
another thing I've discovered, if, these are run as the 809 data sheet indicates for P/P audio use (haven't measured, just speculating at this point), they are running in Class AB . . . discovered this thread over on DIYAudio . . .
http://www.diyaudio.com/forums/tubes-valves/178468-809s-class-b-p-p-w-feedback.html
so I've been organizing the basement and garage, and guess what I found ? 3 more 5R4 rectifiers, and three more 809's (2 of which will need to be soldered into the plate cap, but I'll take it
)NOW . . . if I can just find a cheapy pair of 2A3's, I can get these monsters going in STEREO !
another thing I've discovered, if, these are run as the 809 data sheet indicates for P/P audio use (haven't measured, just speculating at this point), they are running in Class AB . . . discovered this thread over on DIYAudio . . .
http://www.diyaudio.com/forums/tubes-valves/178468-809s-class-b-p-p-w-feedback.html
markus
Master Procrastinator
thanks for looking Don
might go Chinese, since the pair I already have is Valve Art . . .
