Voltage amp for RCA console pulls

[ericc129]

Man, I know this an old thread, but I couldn't help myself. I just discovered and was given an RCA RS177J amplifier. I am also a newbie when it comes to working on anything with tubes; I just know I prefer the sound from a general perspective. I'm currently just looking for pictures of refurbished ones to get an idea where to start since this is going to require rca inputs and new output plugs. Also, any part lists from other rebuild would be great. I'm hoping my sansui AU-517 preamp, or marantz 2238 preamp will be enough to drive it or overcome the gain issues if my aikido struggles.

 

[tonebells]

I have played with one of these amps but never got it dialed in. The gain is very low because the tuner/preamp had a gain stage in it as well. It will play very nicely just at a low volume. One of these day I will try again to come up with something to make the gain better.

Tony

 

[jdsalinger]

http://www.introni.it/pdf/Radio_diagrams_1964.pdf
Page 136 left hand side of the page....is as close to your schematic as you're going to find.

Mine was already recapped with decent 0.27 uF Panasonic film caps for the coupling caps. Not sure I'd have picked these, but the model chosen is supposedly good for coupling.
For filter caps, I used CP-JJ-32X2-500V & CP-JJ-100X2-500V from Tube depot.
Input jacks: Parts express Part # 091-1120 (qty 1)
Speaker binding post; Parts express Part # 090-475 (qty 2)
IEC AC power jack : Parts Express Part # 090-442 (you will also need to install an inline fuse)

 

[Mikethenewb]

I have the original console and tuner for this receiver. The amp has been really hard to work on with all the small spaces that it has. Would you all recommend transferring the entire amp over to another chassis?

 

[jdsalinger]

Dude, even if it WAS cramped, that doesn't make sense.
Besides, as I recall, this chassis is SPACIOUS.

By the way, enjoy. I miss my RCA console. It was BUILT 10X better than any other console I've ever seen.
Strong as heck and the quality of the woodwork and the finish was off the chart.

 

[Dswankey]

I have the....... tuner for this receiver. The amp has been really hard to work on with all the small spaces that it has. Would you all recommend transferring the entire amp over to another chassis?

What it is it you are trying to convey when you say you have the tuner for the receiver? Are we talking the power amplifier? I assume it's a RS-177 based on this thread.

I concur with @jdsalinger the chassis is spacious does it look like this underneath? If so compared to other manufacturer's tube amps it's pretty spacios

 

[gadget73]

heh, I've got stuff that I'd be overjoyed to have that much room inside. Swap the wax caps for modern ones and that will free up some space.

 

[Mikethenewb]

I recapped it. I guess what I was referring to is trying to replace the electrolytics by using the preexisting contacts on the cans. I think I should have taken more time to replace the caps more carefully.

 

[Mikethenewb]

Is it even worth making any mods to the original if I have all of the original components of the console working? I am referring to the mods discussed about gain

 

[gadget73]

If you're using it as-designed with all of the parts you shouldn't need to change anything. The trouble is that in stand-alone form, they don't have enough gain. The extra gain stage is in the preamp, not on the power amp chassis.

 

[mike567]

If that chassis is cramped then try a German radio for a challenge!

 

[John Beeler]

Hi there:
I'm new to this thread too and a real tyro when it comes to refurbishing vacuum tube amps but I'd like to chime in to sing Tom Bavis's praises for his suggested mods to the feedback circuit.
I followed his recs and am delighted with the results.
I'm running a Dyna PAT-4 thru an RS177J powering JBL 4311B studio monitors.
It sounds great and has more gain than I'm likely to use under virtually any circumstances.
No need to change the 6FQ7s out for 12AX7s, much less add another gain stage, even tho the PT could easily handle it.
Unless of course you're trying to power acoustic suspension speakers....

 

[Dswankey]

Wow!! seeing Jays avatar brings back memories, a very cool, generous & humerus dude.

I wasn't aware of this thread, which was long before I got to know him (digitally, never met in person) back in the early/mid 2010's.

Interestingly enough when I acquired my console pull, stock RS-177 in roughly the same time period my buddy/tech restored & modified mine by adding two 12AV6's along with a gain control.

I remember chatting with Jay about my new toy and the 12AV6's my tech added and a couple of weeks later there was a package when I arrived home one afternoon which consisted of a handful of NOS 12AV6's from his personal stash.

I followed up with him to thank him profusely, as I didn't ask for them, and asked if I could reimburse him to which he said no he just wanted me to have some backups in case I ever needed them, I still have them too.

That's the kinda dude he was, AudioKarma at its best!

 

[gadget73]

if you have a preamp with enough output, gain isn't a worry but I suspect in basically-stock form it just wouldn't play too nice with a passive preamp. Probably needs a couple volts to hit full output power. Frankly a lot of preamps have more gain than most amps actually need, so the pairing isn't bad.

I am sort of curious what the stock input sensitivity actually is. Just some very rough guesstimates here, from the input of the first 6cg7 to the grid of the 6bq5 its probably around 15 gain, and this maybe has 10db or so of feedback. If I'm not completely off my rocker here, that should mean that 1 volt in gives about 4.5 volts at the grid. A 6bq5 like this probably needs around a dozen volts at the grid to hit full stride, so I'd expect maybe 2.7 volts or so input to get full output power?