[AMPS] Emiac Y448 and SB220 grid resistor path for high current ps cap discharge.

[Skip S Isaham]

Re: SB 220 interlock(s) and y448 tubes.

Hello there,

With all the interlock/pencil talk going on, I just thought I'd mention
something about the SB 220 circuit.
When using the interlock discharge scheme, the grid resistor (.82 ohm
value if memory serves) becomes a high current path for the capacitors in
the power supply in certain condition. 

This doesn't appear as good practice for the resistor... 

I have removed the interlocks from my SB-220 and rely on time/bleeder
resistors as the primary method for reduction of HV in my power supplies.
Common sense then dictates that an insulated handle shorting bar be used
and large diameter wire (about 12ga)  jumper(s)  be applied across the HV
circuit paths during service/repairs.  All this done long after the AC
mains are removed and secured in visual range.

Inside the Continental Broadcast Transmitter I converted to 1640KHz for
KXBT in Vallejo, CA...  I left the interlocks in.

Rich's SB 220 article confirms my thoughts about the power supply
discharge path when using the factory interlock(s).

Anyone inside an amplifier had better know what they are doing, else the
gene pool filter be applied.  

Based on the quanity of cars using the freeways here in California and
the related road rage, Non interlocked HV power supplies should be
offered free at roadside stands and with speeding/reckless driving
tickets.

Onward...

[snip]
:From: Arthur Moe <kb7ww@chatusa.com>
:To: Amps <amps@contesting.com>
:Subject: [AMPS] INFO: Emiac Y448 looks like 4-1000 tube
:Could someone enlighten me on this please.
:Thanks
:art
:KB7WW

Art, 
I came across two wooden shipping containers full of y448s about 15 years
ago, for sale for $5 each brand new... NOS surplus.
I checked into the tube and found it to be a 4-1000 with slightly
different heater requirements if my memory serves me. Everything else was
similar to the 4-1000 ratings.
I mentioned to the vendor that I'd take the two shipping containers and
that I'd come back next weekend to finish our business and pick up the
tubes.
During the week, the business has a small fire in the back of the yard...
the only major damage were the two shipping containers and a forklift
that were burned to the ground.. For me all that were left was the melted
metal and broken glass in a small black pile... 
Two lessons learned... the details of the y448 at the time and to avoid
delays in dealing with surplus shipping containers made of wood.

73's to you all...

Skip May   wv6f

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