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

[R.Measures]

On Sep 1, 2004, at 8:59 AM, Bill Fuqua wrote:

> That gives me an idea. I have a Thunderbolt and if I go to solid state 
> rectifiers, a capacitive input filter and then wire up the 866A's in 
> parallel but in series with the filtered  output I would still have 
> the light show and more output. Just have to have higher voltage 
> filter capacitors and bypass the filter choke.
>
Bill -- For SSB, this is a good plan -- provided the Tune-C will stand 
the extra potential and the PS filter C is increased in value to make 
up for eliminating the choke filter.  However, with a C-filter, a 
stepstart might be a good idea to limit the turn-on surge.  Also, 
4-400As need c. 800v on the screen to take full advantage of their 
emission.
cheerz

> 73
> Bill wa4lav
>
>
> At 09:17 AM 9/1/2004 -0600, 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. 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
>> _______________________________________________
>> Amps mailing list
>> Amps at contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
>
Richard L. Measures, AG6K, 805.386.3734.  www.somis.org