Author Topic: RCA 4VF488  (Read 2671 times)

garrardfisher

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Re: RCA 4VF488
« Reply #15 on: July 30, 2016, 10:03:18 AM »
Well, by a great stroke of luck, I discovered a source for the schematic to the RC1211A.  It is here http://www.introni.it/pdf/Radio_diagrams_1964.pdf 

It's in Italian and not the best website, but fortunately had a pdf with schematics of many popular brands from 1964.  I'm sure it will be helpful to others who come across this thread.

I started this morning to inspect the preamp and realized quickly that I didn't have C33, the main multi capacitor, grounded.  Silly mistake.  I just figured the cap was grounded through the umbilical to the power amp.   There were no wires left disconnected when I completed my recap, but I think the original can cap had a grounded case that was soldered to the chassis....not a wire to the NEG solder tab.

I grounded the NEG solder post and the hum was gone!  woo hoo!

Now there is still an issue with the tone.  Bass is overpowering and the treble is light.  Sound is boomy and not well defined.  I suspect that some of this is due to the "warmth" of the hi fi of that era, but right now, I have the treble control cranked and the bass control dialed to about 9:00.   I didn't recap the tone control because they use the burgundy film caps, but I'm going to order some replacements and next time I go in, I'll check the resistors too. 

For now, I'm just happy for the huge step forward.  Aside from the tone control, I have to replace the grill cloth and clean and refurbish the turntable.

garrardfisher

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More progress
« Reply #16 on: July 31, 2016, 03:15:23 PM »
Hooray!! 

After studying the RC1211A schematic, I noticed that the TAPE input goes directly into the preamp.  I realized that this would be a good way to eliminate the FM & AM sections and see if the boomy sound originated there or in the preamp. 

So I replaced the "Tape" input jack ( proprietary, 3 pin connector....NOT RCA...go figure  :o ) with some RCA input jacks.
Well, the boomy bass and weak treble is definitely in the FM & AM circuits.  The Tape input didn't sound spectacular, but not boomy and the treble was significantly more clear.   The bass knob could be set at center without blowing me away, but cranking it up to 3:00 would still be too much.  The treble at center sounds pretty veiled, but when it is cranked it sounds pretty crisp and boosted.  I wouldn't want the treble less than 3:00 though, cause it is too veiled.  It may be that it is only the FM that is boomy and weak, but hard to tell with how bad AM sounds anyway.

I think the tone controls could use a recap and maybe some fresh 6FQ7s.  The power amp actually has original (& mismatched) 6BQ5s as well, so now I know that it's worth investing in a new quad and grill cloth.  I was waiting to see if I could solve the hum before getting new ones.

garrardfisher

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Re: RCA 4VF488
« Reply #17 on: September 04, 2016, 08:42:38 AM »
Latest situation. 

Honestly, I had given up on this console because I thought I had reached the end and still couldn't come up with why the sound was so veiled and boomy.  It just wasn't listenable and I love the sound of the stand alone RS177J amp.  But this console is in such good shape and such a high quality classic, I really hated to part her out.

So, even though I had already removed the molex connector for the umbilical from the amp side (to use the hole for the new IEC socket), this morning, I gave the preamp one last-ditch troubleshooting session.  Since there is hardly anything between the tape input and the audio out, I walked through each component, testing values and ensuring new caps were soldered correctly. 

The only things between the tape input and the audio out are:
(1) preamp tubes, which I was able to swap out with the amp and proved all 4 tubes to sound good.  Also cleaned the pins and sockets.
(2) tone control PEC, which I bypassed and still had bloated bass
(3) resistors, which all tested within 10%
(4) caps, which were all replaced with new orange drops.
(5) volume, balance and tone control pots, all of which were sprayed with deoxit and worked hard.  I believe I even confirmed resistance.

The one thing that I overlooked was the loudness PEC (see the brown PEC in the uppermost LH side of the pic in reply  #3).  It is difficult to reach this, since it is tucked into the corner.  This is a 5 pin PEC with...wait for it....common ground pin.  And guess what, it appears to have never been connected...from the factory.  The insulation wasn't even trimmed back. 

At this point, I am excited that I may have found the problem.  Without that ground connected, I'm not sure what the effect would be, but I'll bet it isn't good.  And it may also be that the loudness PEC isn't the greatest, but first, I'll connect the ground and see what that does.

Of course, after giving up on this console, I cut out the original molex connector from the amp, so I'll have to make a run to RS to buy a new 9 pin connector ($6).  Not so bad I guess.

Just wish I could find a punch, cause I'm not looking forward to drilling and filing a square hole (my normal method).  Any suggestions?



garrardfisher

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Re: RCA 4VF488
« Reply #18 on: September 09, 2016, 09:45:55 PM »
Well, FINALLY!   :)

Last night, I wired up the 9 pin molex and connected (for the very first time) the ground of the loudness PEC.  (I still can't believe RCA missed that and that none of the previous owners took it to a technician.  It was totally un-bearable).

But, lo and behold....it sound is normal now.  The treble can sound nice and crisp, but only when the treble control is cranked to the max.  The overall sound is a bit soft/veiled as you'd kind of expect a vintage console to sound.  This is entirely due to the preamp.  The speakers themselves are really very nice. 

I don't dare turn the bass knob up past 12:00 and the treble pot is very muddy below 12:00.  That tells me the PEC for the loudness and tone controls are probably in need of replacement. 

The SQ was kinda disappointing in general.  Driving the console with my Forewatt preamp sounds twice as good as the original RCA.  I mean the speakers rival my Advent 5012's and that's saying a LOT.   The amplifier sounds great as a stand alone too.  The Forewatt has gain of 7 so it drives the 177 just fine.

But all in all, it was worth the effort just to settle in my mind how it sounded with everything connected as it is supposed to be. Just kills me that I gave up so quickly and forced myself to have to go and re-wire the harness with a new Molex connector.  Ugh.  Well, learned a lesson at least.

I really don't see me listening to this much because it doesn't come close to my main rig in terms of Hi Fidelity, but I'm going to hold on to it for a while and think about possibly putting it in another room.  May make this a winter project to redo the PEC. 

Phototone

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Re: RCA 4VF488
« Reply #19 on: November 15, 2016, 10:50:50 AM »
Your 488 is identical to my 480 (see newer post) except for cabinet finish. My cabinet is a pale yellowish wood.  After recapping and a bit of tube rolling and very minor turntable cleaning and lube, my unit plays fine on both records and radio and also thru the external (tape) inputs, which I use for a CD player. I did learn that if your phono cartridge is bad, there are no replacements available.  I suppose the only choice, one I don't have to make, as my cartridge is good, would be to replace the changer with one from previous year which didn't use this "floating" arrangement of cartridge.