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Author Topic: Airline GHM945B suitcase record player  (Read 5835 times)

will316

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Airline GHM945B suitcase record player
« on: January 30, 2011, 08:37:06 PM »
I recently acquired one of these guys and it appears that the power section can be removed and used for guitar. I've found an article that suggested that because this unit only has one transformer that it would be unsafe. If this is true, why? What I wanna do is feed my signal into a Digitech RP-200a floor modeler then into the tube power  section then a speaker. If it can be done, can somebody supply some info on how?
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phatt

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Re: Airline GHM945B suitcase record player
« Reply #1 on: January 31, 2011, 10:52:28 AM »
Yep likely the PSU is connected Directly to Mains. :trouble
You will have to track down an *Isolation* mains Tranny or complete rebuild of PSU might be simpler.
Phil

will316

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Re: Airline GHM945B suitcase record player
« Reply #2 on: January 31, 2011, 04:28:56 PM »
Could you give me a quick explanation? The transformer, tube, volume pot, and wiring is all contained in a metal box that is easily removed(which I've done.) I have 1 RCA in for the needle, 2 wires for speaker and 2 for  turntable motor. I guess what I'm wondering is: how could I isolate it cheaply? Radio Shack carries a transformer that's 1to1(no step up or down) for phone circuits. Could this be utilized? If so, a scheme  or a link to one would be appreciated. Would it be safe to plug this in to my old hi-fi? It has a outlet for aux. equipment on its rear. Is this one isolated for this purpose, or is it there for convenience? Is there a cheap or easy way to build something with supplies purchased at the hardware store? Thanks in advance for any help.
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phatt

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Re: Airline GHM945B suitcase record player
« Reply #3 on: January 31, 2011, 09:09:23 PM »
sorry chum, without a pic or a schematic of the circuit I'm afraid I'll just be shooting aroows into thin air.

All I can say is that a lot of really old valve gear is/was connected Directly to the mains and this is not good practice. (even moreso as the components will be old and prone to failure)

Just ask for what I said a *Mains Isolation Transformer*.
 (a telephone is not mains) :trouble

Why not pull it apart and back engineer it, draw up a schematic and post it here.

For the novice at first it will be hard but rest assured after a while (throw in some reading) you will learn how it works.

Some of the old RCA type books have schematic showing mains connected circuits, you might want to search around.
Phil.

will316

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Re: Airline GHM945B suitcase record player
« Reply #4 on: January 31, 2011, 11:59:23 PM »
Sure thing. I'm kind of thinking of maybe building a pre amp and incorporating this as a power section. A quick, rough explanation is this: Mains>Transformer>Tube>Turntable>Condensor>Rectifier(solid state)>various resistors>Volume pot>Speaker. It's really simple. I assumed that where the signal from the needle comes in I could install a 1/4 plug and go in with my preamp. I'm also wondering if maybe a cheap combo amp could be robbed of its preamp section to be mated with this to be a complete unit. When I figure out how I'm going to utilize this thing, I plan on cloning it if Ilike the sound. The circuit itself is simple and all of it mounts in a box roughly the same size as Radio Shack's metal project enclosure. The tube and condensor are mounted on the outside of the enclosure. The unit claims 45 watts on the turn table. The tube is a 25L6GT manufactured by RCA and has a manufacture date of 3-48(wow!) I hope my limited, rambling info helps.
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J M Fahey

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Re: Airline GHM945B suitcase record player
« Reply #5 on: February 01, 2011, 12:48:55 AM »
As-is it's *very* dangerous (as in it will kill you) and will make anything you connect to it deadly, including your preamp, effects, all cables, your guitar strings, etc.
It was somewhat acceptable (sort of) as a record player because it was contained into an isolated box , it had plastic knobs, and the pickup head (whose wiring you actually didn't touch) made contact only with a plastic record; but with guitars you are actually touching the strings, so .... no no.
Besides it's only 2 watts at best.
To give it any use you'll need a 120-to-120V , 60VA (or more) *isolation transformer*.
You're better off by building one of the AX84 projects, which are *killer* amps, better than most, including Epiphones, Marshalls, etc. and for my musical taste, better than a Tiny Terror, go figure.

Steve Conner

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Re: Airline GHM945B suitcase record player
« Reply #6 on: February 01, 2011, 05:03:05 AM »
Hmm, yes, be careful with that one... A rule of thumb is that if the tube numbers begin with anything other than "6" - or "E" for European tubes - put it back in the dumpster, Salvation Army heap or wherever.

Then again, as a high school student, I managed to shock myself pretty bad, trying to convert a reel-to-reel tape deck that did have 6.3V tubes and a transformer. I still don't know what I did wrong.

J M Fahey

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Re: Airline GHM945B suitcase record player
« Reply #7 on: February 01, 2011, 09:48:06 AM »
Some of these had a *very* small and cheap "filaments only" transformer, specially in 220V countries, where it was prohibitive to reduce them with power resistors.
In 110V countries, the classic tube setup used in record players such as this was : 35W4 ; 50C5 ; 25L6 or 50L6 all in series add up to around 110V, give or take so they caqn "save" on the little one too.
Anuway *all* are deadly.
As an example read:
http://www.tdpri.com/forum/amp-central-station/138221-old-tube-radio-amp.html
Some excerpts:
Quote
YES many vintage radios contain most of if not all of the correct parts to be converted into a guitar amp. It's one of the first conversions I attempted back in the '70s when I was young and naive, I embarked on the endeavor with no documentation and no clue. My victim was a late '40s Philco tabletop radio. I was shall we say in the steep part of the learning curve, I managed to quickly find out firsthand that there was high voltage available everywhere in that thing. I managed to achieve memorable if not fatal electrocution from nearly all available voltage sources in that chassis. Eventually by trial and error I clipped on to a point where the radio weakly amplified my guitar.

I'll pass along a few tips: Converting old radios to guitar amps is the advanced program. It's much easier to start with something intended to be a guitar amp. It's necessary to be able to cull likely donors from unlikely donors. You want a power transformer and an output transformer. If you don't see two transformers PASS on that one. If you see 50C5, 25L6, 35L6 or 50L6 tubes PASS on that one. Fair warning, ignore it at your peril!

Quote
When I consider the risk/benefit ratio transformerless junk just isn't worth it. They were meant to be cheap to begin with and all these years later they're still cheap. Buy and butcher a Valve Junior, it costs no more than an old radio plus an isolation transformer and there's a large and enthusiastic support network for that platform.