Author Topic: RCA 4VF488  (Read 3490 times)

garrardfisher

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RCA 4VF488
« on: April 23, 2016, 09:38:55 AM »
Last weekend, I finally finished the filter recap on my RC1211A tuner and the RS177J amp. 

I removed the hideous grill cloth right away.  I'm considering replacing with a gold diamond pattern. 

This console has the warmest, sound I have heard in a tube amp.  The bass is so full that the dead center position on the bass control is almost too much.  My Maggie 9300s, Pilot 402, KT88SE are all relatively more clear and detailed.  I like clear and detailed, but I have always wanted to have an amp with the "warm" tube sound that everybody talks about.  I suspect that "warmth" may be due to issues in the treble tone circuit.  The treble coming out of the tweeters is really slight, even with the treble knob cranked.  I tested the speakers with another SS amp and they sounded really nice and clear, so I'm sure the preamp tone control circuit needs some attention.

The unit came with all RCA preamp tubes and a mixture of RCA and GE 6BQ5 tubes in the amp. 

Here is what I've replaced so far...
the coupling caps & cathode bypass caps & filter caps in the amp.
the filter cap and cathode bypass caps in the RC1211A tuner/preamp.
the 12uF crossover cap on both speakers with paralleled 10uF (clarity) and 3uF (Dayton) film caps.
Installed brand new JJ 6BQ5 tubes
replaced one of the 12AX7 in the tuner/preamp with a 12AT7 from a Maggie tuner. 
Deoxited all pots and switches.

Before all my recap work, the unit sounded OK, but no hum or buzz.  After the filter cap change, I have a low hum in both channels.
Also (probably not related to the filter cap change) one or the other channel will start to crackle and then cut out after the unit warms up for a few minutes.  I haven't done a LOT of troubleshooting (swapping tubes, etc) so, a solution might come to the surface soon.  Could be a solder joint, but I'm thinking that it may be a tube.  I have already tried plugging into a different power outlet, but that didn't clear up the hum.

At first, I was going to leave the brown film caps alone, but I have read some people say they can be found to be leaky, so I plan on replacing with orange drops in the near future.

Does anyone have a schematic for the RS1211A that they can provide?  I'm really in the dark in terms of troubleshooting.

Also, since I know very little about RCA history ( but am really becoming a fan ) if you know about where this model sat in the line up, I would like to know.  I presume it had to be near the TOTL.  It is VERY well built.  So well built that even though I'm more of a component guy, I feel I have to restore this one.

Thanks in advance!

garrardfisher

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Re: RCA 4VF488
« Reply #1 on: April 23, 2016, 09:43:09 AM »
I would also appreciate it if someone can tell me how to

1) insert photos into my text
2) attach photos that aren't so huge when you open them up?

Larry H

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Re: RCA 4VF488
« Reply #2 on: April 23, 2016, 10:16:05 AM »
I would also appreciate it if someone can tell me how to

1) insert photos into my text
2) attach photos that aren't so huge when you open them up?
The only way to insert photos in your text is to use an outside photo hosting service, such as Photobucket, and post the "for message boards"
link in your text.

For picture resizing, I use PhotoPad Image Editor.  Google it and you will find downloads for it online.  It is free.  I resize all my photos with it so they won't be over about 700 pixels wide.
--Larry

garrardfisher

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Re: RCA 4VF488
« Reply #3 on: April 30, 2016, 12:48:39 PM »
Recapped the tuner/preamp this morning. 
It's got a little hum in both speakers.  I've tried to pull every tube and it seems like the 2 6FQ7 preamp tubes (the ones IN the preamp, not on the amp) make the loudest hum when they are removed. I'm thinking that it has something to do with the heater pins, but I don't remember it humming prior to my recap. 

Also, the original cone mid/tweeters are really really quiet.  I think I'm going to set some Magnavox horns on top and see if they sound any better.


garrardfisher

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Re: RCA 4VF488
« Reply #4 on: May 01, 2016, 08:57:23 AM »
Well, I did a quick test of the console speakers with my Pilot 402 receiver.  Great sound, so I know that there is something funny going on with the RCA preamp or tone control section.   Could be the PEC that makes up the tone control, or a tube.  (need to get a tube tester).

I have some work ahead of me.   :(

spiritofradio

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Re: RCA 4VF488
« Reply #5 on: May 03, 2016, 07:19:56 PM »
I have a 4VF446 with the same changer, tuner and amp.  You need to 'love' that amp when you recap it.  Set yourself up so you can check it after each cap.  also retouch many of the old solder joints.  Lastly, you will almost certainly have resistors that are either shorted or far enough out that they are creating issues.   I took my time ( about a week) to do the amp and the tuner.  I wouldn't part with mine for anything.  Also, the 6BQ5s were pretty well gassed when I got her, so I bought all new JJ's and it really paid me back.  I have the schematic somewhere.  Do you still need it?  And don't let anyone bash that changer neither! lol   I love my Studiomatic.  I teared up when I had to retire the cartridge, but it died and I had to improvise hanging an EV-26 under the floating bracket.
~~~and did you exchange.......
a 'walk-on' part in a war.....
for a lead role, in a cage?~~~

garrardfisher

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Re: RCA 4VF488
« Reply #6 on: May 04, 2016, 05:22:18 AM »
Hey, that's pretty high praise.  I'm glad I didn't toss the Studiomatic!  I actually bought a pairof Dual 1209s to use in there, but the Studiomatic just...looks....RIGHT.
You really renewed my ambition to get this baby ship-shape. 
And YES, I would absolutely appreciate it if you could pass along the schematic. 

I've inserted pics again, so they are more easily viewed.

Thanks Spirit!!










spiritofradio

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Re: RCA 4VF488
« Reply #7 on: May 04, 2016, 10:56:25 AM »
Don't dare put that Kraut table in there!!! lol    Leave the duals for Solid state stuff with preamps made for magnetic carts.  This baby was born for ceramic.  Is that tarnish on the TT making it look yellow?   The real beauty in this set is the chrome!   I don't think another console has more chrome on it than this one.  You also need to change the crossover caps on your speakers.  They  make a HUGE difference in the sound of those 4 ways.  I know the RP 218 TT photofact is already uploaded on this site.  Check for the amp and tuner, they may already be there.  We have lots of RCA fans, and "X" RCA fans on this site, so the materials are out there.  I'll check when I get home if it isn't there and get it to you.
~~~and did you exchange.......
a 'walk-on' part in a war.....
for a lead role, in a cage?~~~

spiritofradio

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Re: RCA 4VF488
« Reply #8 on: May 04, 2016, 06:34:14 PM »
Couple things I found that might help.
~~~and did you exchange.......
a 'walk-on' part in a war.....
for a lead role, in a cage?~~~

garrardfisher

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Re: RCA 4VF488
« Reply #9 on: May 04, 2016, 07:11:49 PM »
Well, I was going to use an outboard phono preamp through the tape inputs, but now that you have encouraged me to revive the Studiomatic, I'm excited.  I really do like the looks of it.  (well, that and I don't want to be shunned either  ;) )

Thanks for the docs.


spiritofradio

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Re: RCA 4VF488
« Reply #10 on: May 04, 2016, 07:22:46 PM »
its a djvu file.  If you continue to restore vintage equipment, there is a great resource out there that only utilizes this viewer.  just google the djvu viewer and you'll find the link to the site you can download it.  It looks like a spam site but it's not.  once you have the viewer you can open the file.  It will come in handy like i said if you keep doing this sort of thing.  I think the photofact is in the download section of this site.  Look under Vintage record changers, and you want the one for RCA RP-218.  That's your changer.
~~~and did you exchange.......
a 'walk-on' part in a war.....
for a lead role, in a cage?~~~

garrardfisher

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Re: RCA 4VF488
« Reply #11 on: May 17, 2016, 08:10:39 PM »
Thursday, I'm going to add RCA inputs & binding posts to the amp.
Not planning a "pull", just wanting to hear the amp itself and to isolate the hum I'm hearing.

Can't wait to hear this.  It looks to be a step up from the Maggie 9300's I've worked on.

garrardfisher

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Re: RCA 4VF488
« Reply #12 on: May 20, 2016, 08:13:46 PM »
Well, the amp is now a stand-alone.  Last night, I tested it on my Advents and wasn't too impressed.  Tonight I enjoyed an entire night of running it on my Pi 3s.  Pretty good, but very smooth and maybe a little veiled. 

I was driving it with my Forewatt preamp (no tone controls).  It was pretty smooth and I could hear good detail at times.  Snare drums sounded great.  Female vocals were set back and veiled.  Sound stage, 3-D, placement of instruments was not the best.  My KT88SE was much better.

So, cool amp.  Very cool.  Maybe the fact that the guy who "recapped" it for the PO used all Panasonic film caps.  I've not heard of them being choice for recap jobs. 

I may give a shot to replacing the signal path resistors with carbon film and replacing the Panny's with something nicer in the signal path only. 

I'm almost ready to pull the trigger on a Decware SE84 or maybe build a 45 SET amp, but I would love it if I could tweak this baby just a bit more for some clarity and open-ness. Nice big PT and larger OPT than a Magnavox. 

Oh, and by the way, the humming is definitely NOT on the amp.  This thing was DEAD quiet!   :)

garrardfisher

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Re: RCA 4VF488
« Reply #13 on: June 09, 2016, 04:33:42 AM »
I found a loose wire on one of the + terminals of the filter cap in the preamp.  After re-soldering it, the hum is much less noticable, but not entirely gone.  So, at this point, it isn't dead quiet when there is no audio ( tape or phono modes ) but it seems stable and the hum doesn't interfere with the music.

One other issue is that the bass is overwhelmingly full and the treble is weak.  I have the treble dial turned fully CW and the bass at about 9 o'clock just to get a tolerable sound. 

I want to try replacing the tone control PECs.  One number I read off the PEC was RCA 972118-4 (there may be more...I just read what I could with the preamp installed). 

I was able to get a RCA 106457 PEC schematic from Tom Bavis on the AK website.  He said that came from a couple of his RCA console schematics.  I'm guessing that typically a mfr would use common PECs like this in all of their tone control networks.

garrardfisher

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Re: RCA 4VF488
« Reply #14 on: July 04, 2016, 03:12:00 PM »
Well, I bypassed the tone control circuit just to see if the sound cleared up at all.  No luck.  Left channel is much more quiet than the right channel.  I tried both FM and AM.  FM is really really bass heavy and the left channel is weak.  On AM, the channels are more clear, but the left channel is still weak.

I have now eliminated as sources of the problem:

1) the power amp
2) the speakers. 
3) preamp tubes (same ones are used as preamp tubes in the power amp.  Swapped both pairs and got great sound using the power amp w/o the tuner/preamp)
3) the tone control circuit and PECs (well, they MAY still be bad, but they are not the only cause of the heavy bass, light treble and weak left channel).

I can't give up now, but I would appreciate any suggestions on what to do next, since I don't have an O-scope or a schematic.  Obviously, the source of the problem is down from the volume pot. 

I'm thinking that one of the preamp caps that I didn't replace is potentially bad.  I guess I could try using an aux input to see if it is just something in the AM or FM circuitry.