Converting Stereo Console into guitar amp with aux input.Need ideas

[jtbullet]

Hi. I have a gigantic 1970s era rca victor stereo console. It has a hinged lid with a turntable and tuner inside. I am replacing the power cable that broke off, and then I will see if it still works. I assume the electronics will still work, which will let me evaluate the speakers, which I assume will not work very well. It has been incredibly well stored, so it may all be fine.

My end result would be to convert this thing into a big guitar amp, by replacing the speakers and then the internal electronics with a nice guitar head. I would also like to retain its use as a home entertainment unit, by including a new audio input (for whatever - ipod, pc). Where would YOU begin?

[Keriwena]

I'd begin by making the decision between guitar OR hifi.

Both guitar amps and speakers distort in ways that keep electric guitars from sounding like what they really are - steel strings on a plank of wood. I suppose if all you listen to is Chuck Berry and Elvis, and you want to recreate the sound of a '57 Chevy radio at full blast....

Guitar speakers don't go low enough to reproduce bass guitar and they barely go high enough for vocals. What they do to cymbals is literally painful. Guitar amps are all about bass and treble boost, and to get a typical guitar amp (Fender, Marshall, etc.) "flat", you need to turn the bass and treble controls to near '0'.

On the other side of things, you can't use hifi speakers for guitar. The suspension is linear, and simply can't handle the dynamic range a guitar can produce. Nor are they designed to deal with the heat that distorted guitar signals produce. Same thing with hifi amps. No one "dimes" a hifi amp for hours at a time. They're meant to work up to their rated wattage, not far beyond.


Having said all that, I have spent quite a bit of time listening to music through guitar amps. The best rig was a home-brew copy of a Fender preamp running into a Dynaco Mk III with a JBL D130. Clean speaker, keep the amp down... it wasn't that bad, but then the cassette tapes of old Chess recordings didn't have a whole lot of fidelity to lose.

[jtbullet]

Ok, a little more specificity. I am mostly outgrown of my need for a marshall stack. I have begun the process of opening up my console. It's a rca victor vft-76w. Its got some 12axt tubes. One channel is playing, one is not. I suspect either the tube or the crossover for the right channel is bad, but thats a shot in the dark. Each "side" of the console seems to have 4 drivers, a 12" and 3 similar sized appx 4" units. Probably 2 mids and a tweet or 2 tweets and a mid. The wood is showroom condition though. It's high quality and built like a tank.

For now, I believe I will begin the process of replacing the speakers. I will buy a couple of the dayton audio small amps to power them so that I can listen as I decide what to do with the 12ax7 based amplifier. I have no desire to use the original turntable and tuner, as the radio will turn on, but there is some serious hum right from the start even with the volume new. I would love to salvage the tuner, since big, smooth turning knobs are nice.
For now...can anyone recommend replacement speakers?
bass - its a 10 or 12 inch
mid - 3 - 4 inch
tweet 3-4 inch

Basically I am looking to create a high quality free air system since its basically a backless box. The wood the speakers mount to is removable, so im not tied to using the same configuration. I'd love any recommendations.

[Pano]

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Plenty to choose from there. Good for guitar, not ideal for hi-fi. Maybe you could put in a switch for tweeters to use when you want to listen to recordings. Sounds like you want it mostly for guitar, so build with that in mind.

Keriwena's post is full of good advice.

[jtbullet]

Well, i have thought it over...I am going to use it for reproduction, and just get a fender twin or similar for guitar. But now, on to replacing the 12ax7 amp...do you think a couple of dayton audio units would do the job? I wont play it loud, but id like good transient capability.

[Pano]

Which of their units? The Class-D amp? It's decent and will hold you. But you should fix, or get fixed, the tube amp. 12AX7 is the input tube, do you know what the output tubes are?

[jtbullet]

I am not totally sure. I'm kind of new to all this. It's a vft-76w rca. I will take pics tonight, and dig up the photofacts schematic. I was truthfully thinking about the 90$ class t, 50 wpc model, since its cheap and I think its going to take some time and money to sort the 12ax7 amp. I figure crossovers are going to cost me dearly. I was hoping to make up for some of the electronics costs by finding other "hidden gems" like the popular small tang band units. crap for the money of good passives, i could use a decent active, and run a ton of tri path amps, 1 for mids, one for tweets, run a monoblock for subs. I'm open to ideas though. I'm not a gear elitist.

[DrDyna]

Crossovers shouldn't be too expensive if you stay away from boutique parts.

[jtbullet]

Well, thats kind of where I'm at, replace the speakers (daunting), buy decent crossovers, add some small amp. Make it all useable while researching amp repair. The fact that it made sound at all was nice. If a tube is bad, is it usually visible? I thought:
1) Pull the bad channel's tube and look at it
2) put the good channel's tube in and see if it works
3) connect a known speaker to the good channel to see what the sound is like
would be good places to start dissecting the problems

[Pano]

Yes, that's the basic trouble shooting.
The $90 class-d amp is decent and should hold you for quite awhile. I use a little Lepai class-d in my old Fisher console 'cause the tube amp was gone. Works great, it's my TV speaker.

Why replace the speakers? Get it working first and listen to them, you might like them. Add a small resistor in series to mimic the output impedance of the tube amp. Maybe 2 or 3 ohms. Grab a few from Parts Express when you order the amp.