[Amps] 4-400A and QB4-1100 amp - TSPA

[R.Measures]

On Sep 1, 2004, at 8:17 AM, John T. M. Lyles wrote:

> The 1960 vintage Heathkit Chippewa amplifier model KL1 was a dual 
> 4-400A amplifier which worked well in class AB1. It was described in 
> Electric Radio magazine a few years back, with some modifications to 
> improve it. I believe that there is an online index to ER which you 
> can look up, and order a back issue. I believe that earlier W6SAI 
> Radio Handbooks (like 21st edition) elaborated on the craft of 
> building tetrode amplifiers. About that time the 3-500Z was really 
> becoming a favorite, as a grounded grid zero bias (low bias) class B 
> amplifier. Setting up tetrodes for best IMD and linear operation 
> requires a bit more care, as you have both a screen and control grid 
> bias voltage to deal with. Some have found that grounding the grid and 
> screen for RF (and applying the DC bias to both) and driving the 
> cathode is a good way to handle a 4-400A.

J. T. --  For a g-g 4-400 or 4-250, DC bias is needed for obtaining 
enough ZSAC (75mA min) at lower anode supply voltages, however, at c. 
3500V-DC, no bias is needed.

> The Johnson Thunderbolt amplifier had 4-400As but it ran them in AB2 
> at too low an anode voltage, leaving it short of output and prone to 
> being overdriven (causing IMD).
>
> I have a Chippewa that I am going to restore someday, as it got 
> "modified" by someone. I saw another one that had been converted to 
> grounded grid, but wasn't interested as it had been too modified from 
> original, and for that an SB220 or Drake L4 would be adequate. Problem 
> with Chippewas is that they had a separate huge power supply chassis 
> with 866As and it is usually missing or burnt up.
>
> 73
> john
> K5PRO
>
>
>
>> Message: 1
>> Date: Tue, 31 Aug 2004 18:23:08 +0200
>> From: "ON5KM" <on5km at planetinternet.be>
>> Subject: [Amps] search 7527A design
>> To: <Amps at contesting.com>
>> Message-ID: <005601c48f76$d160a020$a284efd4 at computer>
>> Content-Type: text/plain;	charset="iso-8859-1"
>>
>> hi ,
>> who has a link or info to a good stable design using 1 or 2
>> 7527a's (qb4-1100 or 4-400) ??
>> all info welcome .
>> tnx on5km stef
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Richard L. Measures, AG6K, 805.386.3734.  www.somis.org