[ARC5] T-22 Woes

[Fuqua, Bill L]

I once built an amplifier with a bunch of 837 tubes in parallel grounded grid. Was a teenager then. 
Similar to building one with modified 1625 tubes. Anyway I paralleled 8 and had around 900 volts plate supply.
I used a surplus roller inductor, don't know where it came from other than I got it from a fellow ham. 
I just could not get the pi network to tune. It was not until after I scrapped it I realized that one side roller slide 
tap was connected to the end of the coil with a strap. It was never in the circuit. The way I wired it plate and
loading capacitors were connected directly by the  strap. Actually, before I scrapped it I tried a single 715 pulse modulator tube.
 It did not work either I felt pretty silly after that but went on build otheramplifiers that did work.. 
Pair of 813s  driven by CE 10A and a pair of 6146B's
Pair of 250TH in grounded grid. Unfortunately,as a silly teen I scrapped an HT-4, for power supply parts and
plate capacitor. driven by CE 10A and a pair of 6146B's
A pair of 4CX250B's, driven by my 10A
And really odd one,Four 6AG7's pressed into a drilled out aluminum block heat sink driven by a CE 10A
   

73
bill wa4lav

________________________________________
From: arc5-bounces at mailman.qth.net [arc5-bounces at mailman.qth.net] on behalf of Mark K3MSB [mark.k3msb at gmail.com]
Sent: Tuesday, June 11, 2013 8:10 PM
To: David Stinson
Cc: ARC5
Subject: Re: [ARC5] T-22 Woes

Hi Guys --

Used the scope as Ian suggested.  I had it out today and was probing with a
pickup loop.  I then remembered that I used a loop when I was working on my
5100 and it provided not so clean waveforms when the transmitter was OK.
So, used the coupling cap....

I used a 33 pf coupling capacitor as it was the lowest I had with a 1 KV
rating.

Measured at the output of the transmitter (external antenna terminal)
before the matching capacitor and 4:1 UNUN:

If using a 67 pf matching cap:  Waveform is clean and about 12V P-P
if using a 100 pf matching cap:  Waveform is clean and about 10V P-P

The outputs on the other side of the matching caps are really, really small
(remember I found the 67 pF cap works great with my other T-22).

The roller inductor has no effect throughout it's entire range.
The antenna coupler has no effect throughout it's entire range.

I listened to my signal on the 756 and it sounds a bit rough, but not to
bad otherwise.

Well guys, I've had fun today working on the radios and I'm bushed so I
think it's time to call it a night.

BTW, to clarify a previous email,  I and now (I had mistyped "not") using
the keying and voltage divider as per Dave S. and the manual.

73 Mark K3MSB






On Tue, Jun 11, 2013 at 6:55 PM, David Stinson <arc5 at ix.netcom.com> wrote:

>
> I'm betting your tank is not resonant due to Hi-Z contacts.
> This is a very common problem.
> Check the screws that mount the variable caps,
> tank coil and roller coil, especially those that are supposed
> to provide grounds.
>
> Ground one end of your ohmmeter.
> Probe the top tank coil contact.
> It should read grounded.
> If it does not, check the connection at the bottom of the tank coil.
>
> Next,  open the bottom of the rig.
> Gently probe the stator plates of the two front-most variable caps.
> Probe the plates, not the end contacts.
> All the stator plates should read at DC ground (through
> the tank coil).  If they do not, a Hi-Z contact point has
> developed between the stator plate stack and the metal
> strip pressed onto the end of the stack as a connnection point.
> Solder one of the pressed connection points with a sturdy iron, being
> careful not to destroy the plastic
> beads that mount the stators.
>
> Hope this helps.
>
> 73 Dave AB5S
>
>
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