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RCA console amp RS193D...

knockbill

knockbill

Lunatic Member
Got this little amp for teh OPTs,,, SE 6BQ5s, 6EU7 driver, 5Y3 Rectifier... I was running it and sounds pretty good, but is all original, so caps should be changed to use it...
Question is, the first cap is 80uF, which seems pretty high... Does this sound reasonable?

Regards,
John
 
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Hey Tom...
Its OK to use 80s,,, however the 1st cap after teh rectifier has a specified max value...
Manual says 20uF for 5Y3, unless plate impudence is raised, however, 80 seems pretty high,,,

Regards,
John
 
If the transformer is wimpy enough, 80 uF is OK. peak current is what matters - so if the winding resistance is high enough, peak current won't be near the limit, even with 100 uF. Don't try it at the maximum rating of the tube with a hefty (low-resistance) transformer unless you like fireworks...
 
Tom Bavis said:
If the transformer is wimpy enough, 80 uF is OK. peak current is what matters - so if the winding resistance is high enough, peak current won't be near the limit, even with 100 uF. Don't try it at the maximum rating of the tube with a hefty (low-resistance) transformer unless you like fireworks...
Click to expand...

Thanks for teh explanation,,, the trans is not big in this thing, but 80 seemed high so I looked it up...
I'll get the hang of this, sooner or later!

Regards,
John
 
Another question,, the OPTs have a screen tap on them,,, Can they be used on a regular SE amp, without connecting teh tap?
OPT leads ohm out to...
Red (B+) to Blue (Plt) 303,,, Red to Brown(screen) 44.5,,, Blue to Brown 347...
I want to use the output transformers on a different amp, B+ and plate...
Any downside to not using teh screen tap?

Regards,
John
 
they can, or you can use the screen tap for lower distortion. It basically makes it an ultralinear output stage vs pentode or triode.
 
gadget73 said:
they can, or you can use the screen tap for lower distortion. It basically makes it an ultralinear output stage vs pentode or triode.
Click to expand...

Figured as much,,, but wanted to try em on teh amp with the gas regulators,,, Can't use both,,, Just wondering if they would be better than teh tx on it now...
Is that screen connection just a tap or a separate winding?

Regards,
John
 
The screen tap is for hum cancellation - it's not connected the same way as UL - and anyway the ratio is too small for UL. But it gives you two choices for primary impedance.
 
But, will it work as well as an SE tx of the same size, without using the screen tap? I got the amp for the OPTs, they have the primary resistance I want...

Regards,
John
 
an ohm check ought to do it but the schematic shows it as one coil. If it reads B+ to both plate and screen wire, its the same coil, or at least its internally connected in such a way as to make no difference.

http://audiokarma.org/forums/attachment.php?attachmentid=183940&d=1260520353


I see what Tom means now. I was thinking screen tap like a regular UL rig, not the humbucker configuration. AA5 tabletop radios used stuff like this. Should be a simple matter of taping off the other connection and calling it a day.
 
I think Tom was saying that either it can be wired blue to red or blue to brown, to get teh closest primary impedance... Seems Red is teh CT, teh way it ohms out?? Also, Red isn't necessarily connected to B+, depending on which taps are used,, so I'd have to try it, to see which secondary lead connects to the FB loop...
If this just has one primary winding, with a tap, its not wound like a PP trans, which has two primary coils, with and end of each connected as teh CT... even tho it has the same primary wire color code...
This must be how its wired...
Starting to get it now,,,

Regards,
John
 

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That's not ultralinear, it's a scheme to reduce power supply ripple to the speaker. It's a trick to balance out the plate resistance of the output tube against the filter cap connected to the screen grid, via the 3900 ohm resistor, R208 or R217. This, along with the turns ratio. should balance out the ripple currents, thus any ripple voltage seen by the speaker is cancelled out.
attachment.php

RCA and others used this scheme in AA5 AM tube table radios as well.

If you wanted to make this amp into a triode connection, you'd have to find out what the plate resistance of a 6BQ5 is in triode mode, and scale R208 and R217 linearly accordingly.
 
Thanks for replying,,,
I picked this amp up really cheap, just wanted teh OPTs,,, The load resistance is 4500ohms, which should work for teh SE 6L6 amp I built... The tx are nice size, and sound pretty good on teh RCA,,, just trying to see if they would work OK on teh new amp... If not, I'll leave them, and rebuild teh RCA...

Regards,
John
 
Usually ultralinear taps are around 43% of the plate lead from the B+ lead. In this case you could use these transformers as partly ultralinear, if you connect the brown lead to B+, the red lead to the screen, and blue wire to the plate. Or you could get a triode connection with a little ultralinear thrown in, if you connect the brown lead to the plate, the red wire to the screen, and the blue wire to B+. Single ended transformers don't care which way the DC goes thru them, thus this "backwards" arrangement will work fine. But be sure to flip the speaker connections to get the feedback look back to negative. Though I don't see any feedback in this amp. And R217 and R208 would connect to B+ directly.
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I confused ya,,,again!!!
No FB in the RCA amp, but there is in the amp I'm working on, I figured it didn't matter which way the OPTs were wired, just wanted to make the most use of them,,,If they work OK Blue to Brown, then I'll be using the full primary winding,,, probably doesn't matter, tho...
Here"s teh build I was thinking of trying them in, if you're interested...
http://www.audiokarma.org/forums/showthread.php?t=598368&highlight=heathkit+A9

Regards,
John
 
Update,,,
Needing a pair of output transformers to use for a build, I took this guy off teh shelf and replaced the PS caps, resistors, and coupling caps, and ran it freshened up, to see how it could sound... It really sounds good!! Lots of Bass, good Highs, no noticeable distortion on teh scope... I did a search on this chassis, and found a few threads on AK where guys got this same amp, for parts, guitar duty etc,,, and after listening to it, decided it should stay as is...
Think I'll put in a switch, and a couple sets of input jacks, and let it live as God intended!!! Its the only 6BQ5 SE amp I have, and is pretty impressive...
This is the reason I have so much trouble finding iron, I guess!!!!!

Regards,
John
 

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