[Amps] Drake L4B to 6 Meters Help

[mikflathead at aol.com]

 I saw this on Eham.com for sale.SB 220 converted to 6 meters only 
as per QST April 08 minus vacuum 
variable
900 watt output. with paperwork, 
very nice. taking offers, pickup 
only zip  
 

 

-----Original Message-----
From: Michelle <michelle_melt at windstream.net>
To: amps <amps at contesting.com>
Sent: Mon, Dec 12, 2016 3:55 pm
Subject: [Amps] Drake L4B to 6 Meters Help




I have converted an SB220 and a TL922 for 6M. Both will produce 1300W PEP 
6M.
( FYI I have converted an SB200 and that gave 600W PEP)

A stock L4-B will easily produce 1KW PEP on 10m and should do the same on 
6M.

Note:
You need to ground the grids directly.
You should use a PI (not T) on the input with the PI output cap right
next to the cathode. I use compression trimmers.
You should reduce the turns on the plate choke and cathode choke to
about 1/3 of what they were originally.
You should use an L-PI on the output. The L is necessary to overcome
the output cap of the tubes. I used the original TUNE cap with most
of the plates removed, and a new LOAD cap.
The open frame antenna relay should work fine. You will need to add a
little cap, maybe around 10pF, on the normally closed path to
compensate for the relay inductance when the amp is bypassed.

- Paul  KW7Y

Paul,    Grids are directly grounded, I will try again the PI input (the 
output cap is next to the cathode), Plate choke was rewound with 42 turns of 
22 ga on 1" porcelain form, I used the stock cathode choke it is 20 turns 
each leg on 5/8" ferrite core ( your saying to make this about 7 turns?) I 
got rid of the open frame relay and replaced with vacuum relays.

Michelle 

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