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PT selection for Gibson Skylark

2/21/2003 7:35 PM
PT selection for Gibson Skylark
hey folks,  
i'm contemplating building a gibson skylark. contemplating because i'm not sure whether its even worth it since originals can be had for quite cheep and i could do any mods i want on that.  
anyway, the schematic i have is here:  
how do i determine which power transformer to use here? that is, i need something with ~300-0-300, 5, and 6.3VAC taps, but how do i know what currents these should run at? also, which is better, one with 280-0-280 taps, or 310-0-310?  
much thanks for help!  
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2/22/2003 5:22 PM

You'll need 50ma or a little more high voltage current, 750ma from the 6.3v, and 2 amps from the 5v. Either the 280 or 310 will work.  
Find an old V/M tape recorder on ebay and you'll have both trannys, tubes(with an extra 12A_7 or two)and sockets.  
This configuration is the same as Fender's tweed Champ(5E1, 5F1)and Princeton(5F2, 5F2A).
2/24/2003 2:41 PM

Thanks for the response...  
aside from knowing that the skylark is like the Champ, how do you determine what currents to run at? Is it from the tube specs?  
also, what is a V/M tape recorder?  
much thanks again :)  
2/22/2003 6:37 PM
Bruce /Mission Amps

Pardon me please, but that little NOS TRIAD power transformer I'm selling on my website (I've used it for small powered 4-10 watt amps for a couple years) would work good for yours too, if you use a 5AR4 instead of a 5Y3, however, I use solid state recitfiers with it myself for about 335vdc to 350vdc output under load.  
Unfortunatly, I only have three or four left.  
2/24/2003 4:42 PM

Yes, the current draws are taken from the tube data.  
Voice of Music made a lot of heavy-duty consumer electronics from WWII until Asian solid-state stuff did them in(in the early 70's, I think). The tape recorders (model 710 through model 722)are all close to perfect for small single-ended guitar amps. I must confess that I have six of these(one turned into a 5F2 and five in the attic at present) All have a 5Y3 rectifier and at least 2 12AX7's plus at least one 12AU7. For the output tube, I believe that all 710's had a 6V6, 714's have a 6V6 or 6L6, all 720's have 6L6, and 722's have 6L6 or 7591. The 722's have 4 12AX7's and 2 12AU7's. All tubes seem to be Sylvania, Westinghouse, GE, or RCA, usually marked "VM". They also have an eye tube which monitored recording level. The 710 and 714 have the longer red-eyed tube and the 720 and 722 have the short green-eyed tube, IIRC. As with much reclaimed audio equipment, the weak point for conversion to a guitar amp is probably the output transformer. These are a bit beefier than most, however.  
The 720 and 722 were stereo and had a companion extension amp and speaker in a separate cabinet(the same size as the recorder). These extension amps have a small self-contained amp with a 6X4 rectifier, 12AX7 and 6V6, small PT and dinky little OT all contained in a 7 X 7 X 3 chassis. This makes for a very dirty little low-powered guitar amp right out of the box. I noticed that last week someone listed one of these as a "PA Amp" on ebay and drew a higher price than the recorders usually sell for. Not a good deal. Someone has done the same this week.  
These recorders usually go for $25-75; shipping can be as much as $40 as they are heavy. There are a number of VM collectors, so the well-preserved ones go high. The 710 that I built my 5F2 from cost me only 7.50 plus $16 shipping. The fabric had been stripped from the cabinet and it looked like it had sat in a damp basements and hot attics for years. The plastic control knobs were melted and the motor didn't run. These were well-built, though and the stuff we're after for guitar amps tends to outlast the tape transport, etc. All of the six I have bought powered up and produced sound right out of the box.
2/27/2003 6:30 PM

thats some really interesting stuff. I looked on ebay for VM products and got a couple of the "PA amps". 25 bucks with a couple more days to go. I didnt find any of the 710-722 model recorders though and these are the ones easily converted into Champs or Skylarks. I'll keep looking...thanks again for this info. really cool :)
2/27/2003 8:48 PM

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