Kay 703-C isolation transformer

[PRR]

There was some confusion about that jumper.

> ground symbol indicates same tie point, right?

It could also mean "to chassis anywhere". You have seen chassis randomly peppered with soldered grounds.

In this case secondary needs to go to C6c, does not need to go to chassis except incidentally thru B-.

There could/should be three chassis connections:
Wall-cord green
PT case (not shown)
Input jack shell

No, certainly not wrong, but could be mis-interpreted.

[punkykatt]

Here are the voltage readings from this amp with the 50va isolating transformer installed.

V1 18GD6A
  pin 5-  P  =  32.9v
  pin 6-  g2=  20.7v
  pin 7-  K  =    0.0v

V2   60FX5
  pin 7-  P   =  140.4v
  pin 6-  g2 =  125.7v
  pin  1-  K  =      5.0v

V3   36AM3
  pin 5-  P  =  122.5vac
  pin 7-  K  =   144.8v

[DummyLoad]

Here are the voltage readings from this amp with the 50va isolating transformer installed.

V1 18G06A
  pin 5-  P  =  32.9v
  pin 6-  g2=  20.7v
  pin 7-  K  =    0.0v

V2   60FX5
  pin 7-  P   =  140.4v
  pin 6-  g2 =  125.7v
  pin  1-  K  =      5.0v

V3   36AM3
  pin 5-  P  =  122.5vac
  pin 7-  K  =   144.8v

FYI, 18GO6A is actually a 18GD6A. it's hard to see that in the penmanship in the original schematic. there is no tube type with designation 18GO6A. 18GD6A is close to 6AU6A characteristics; has same base; exceptions are B+ and filament rating and 2x the plate resistance.


clarified schematic as per PRR recommendation. see attached.

--pete

[punkykatt]

Pete, sorry bout that. Yeah the hand writing on the schematic is sloppy. I was copying my voltage readings I had put on the drawing and copied those tube numbers.   Thanks for the correction.

[DummyLoad]

punkycatt, thanks for posting the voltages of your amp. i included them in the last schematic revision: i hope you don't mind...


--pete

[punkykatt]

Pete. not at all, that`s why I posted them.

[dneace0012]

I know this is an old thread, but does anyone know where I can get some tube sockets for the 703c? All the ones I find online don’t have wide enough mounting hole spacing. I’ve broken a couple of the tabs off mine changing the filter caps. Thanks in advance.

Daniel

[sluckey]

here...

https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=wafer+tube+socket&_sacat=0

[dneace0012]

here...

https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=wafer+tube+socket&_sacat=0

Thanks.  I've looked at those.  The ones that list the mounting hole distance all say 1 inch on center.  Mine is more like 1.25.

[sluckey]

Well, you'll need to drill out the rivets to remove the old socket. So just drill new holes for the new socket.