Picked up a 1957 mono Magnavox 142-BC a couple of months back. I've been thinking about making it into a guitar amp. It uses four 6V6 GT tubes in a push pull set up. Would it be possible to separate it into two channels, one clean and one not so clean that use 2 tubes each?
The 142-BC is only a power amp. A very fine power amp! Do NOT start cutting it up!!
A quad-team of 6V6 can be a very fine sound.
For guitar you need a preamp in front.
A "two channel guitar amp" is (almost always) two *preamps* into one *power amp*.
So build two preamps, mix/switch them into the Input of the AMP142AB.
Yes, it would be "possible" to make two power amps out of the 142AB, but you would need to scrap the probably-fine output transformer, buy two new output transformers, add an additional 12AX7 for 2nd channel driver, and it still would not be a guitar amp without preamps.
The "Tuner Power socket" can supply power to a reasonable number of preamp tubes. (Or a JFET or opamp: it has 18VDC bias on the heater lines.)
Has it been smoke-tested yet?
You WILL convert the wall-cord to proper grounded 3-pin chassis grounding.
A quad-team of 6V6 can be a very fine sound.
For guitar you need a preamp in front.
A "two channel guitar amp" is (almost always) two *preamps* into one *power amp*.
So build two preamps, mix/switch them into the Input of the AMP142AB.
Yes, it would be "possible" to make two power amps out of the 142AB, but you would need to scrap the probably-fine output transformer, buy two new output transformers, add an additional 12AX7 for 2nd channel driver, and it still would not be a guitar amp without preamps.
The "Tuner Power socket" can supply power to a reasonable number of preamp tubes. (Or a JFET or opamp: it has 18VDC bias on the heater lines.)
Has it been smoke-tested yet?
You WILL convert the wall-cord to proper grounded 3-pin chassis grounding.
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I do have the 165-AA pre that came in the console. I brought it up on a dim bulb tester, it passed with flying colors. Yes, I will do a proper chassis ground.
My son is the guitar player. He plays a lot of hard rock and heavy metal. Right now he has a Vox Cambridge 30R, and likes Orange and Blackstar amps. He usually plays thru a Line 6 Pod.
Hmm, high gain circuits can be a bit challenging.
I'm not familiar with the Blackstar circuits ( I think J M Fahey might be) so I can only suggest some "older" circuits:
1. The JCM800 (see RobRobinette who has recently added a 1W JCM800) which is the reference amp. I'd keep everything up to and including the master volume and feed that into your amp.
2. With a little more trepidation (as it has a reputation for being sensitive to build) one could go with a Soldano (see here for, again, a low-watt version that you can snip everything left of the power tubes from). At least here the tone is all in the pre-amp for the high gain channel.
Which brings me to the ugly rumours around metal and the use of tube screamers maxed out before the amp😱. Plus you're never, ever going to get 4 x 6V6 cranked out for more than 60 seconds on a decent quadbox before someone calls the cops
My current "metal-lite " set up is a Runoffgroove Thor into a 2 x 60W SS amp driving a couple of cabs (15" + 12"). Plenty of "chug" available 😀.
I understand the Thunderbird is even better but can't comment myself
My first "DIY" guitar amp happened in about 1962 or so when my parents ditched their Magnavox mono HiFi console for a bigger Silvertone stereo console. The Maggie was from about 1957 and sounded like the little brother to yours. One 5Y3 and two 6V6's drove two speakers, one probably 12 inches, and a smaller one, maybe 3 or 4 inches. I simply cut a guitar cord in half and connected the wires right up to the tone arm where the pickup was.
Now this was the era of surf music and I lived in Florida, so that's what I played. The fab four hadn't hit Miami Beach yet. No reverb though......I remember it being quite a bit louder than my friends Fender Champ, and some people thought that it had a better sound. I would use it for a year or two, until I learned how to make real DIY amps with parts from discarded radios, TV sets, and HiFi's.
Now this was the era of surf music and I lived in Florida, so that's what I played. The fab four hadn't hit Miami Beach yet. No reverb though......I remember it being quite a bit louder than my friends Fender Champ, and some people thought that it had a better sound. I would use it for a year or two, until I learned how to make real DIY amps with parts from discarded radios, TV sets, and HiFi's.
I'll probably just go ahead and rebuild the amp as it is and let my son try it using his Pod. If is doesn't have enough volume or he needs more tone control, I'll build a pre.
This amp is from a small 1957 console I bought for $10. I knew the amp could be made into something cool, but the real find in it was the 15" full range speaker. After some research it turns out it was designed by Peter Jensen and was a precursor to the Jensen P15N. I mounted it in an open baffle and powered it with a Sansui 881. Let the boy plug in his guitar and was impressed by how nice the thing sounds. My son has now made this his practice rig. It should sound even better on tubes.
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