[Hammarlund] Ballast tube replacement....

[Ed Tanton]

I too would like to see that article/schematic. Thanks 
-- 
Sent from my Android phone with mail.com Mail. Please excuse my brevity.

D C _Mac_ Macdonald <k2gkk at hotmail.com> wrote:

Although I have several spare 4H4-Cs, I would appreciate a copy of that circuit and its part numbers.

73 - Mac, K2GKK
callsign at hotmail dot com

Sent from my iPad

On Jul 6, 2013, at 11:52, "Kenneth G. Gordon" <kgordon2006 at frontier.com> wrote:

> On 6 Jul 2013 at 11:26, Charles Ochs wrote:
> 
>> Of course all these old radios will suffer from changes in AC input
>> voltage to some extent.The R-390 (dreaded 3TF7)and the HRO-60 (dreaded
>> 4H4-C) included current regulator "ballast" tubes in an attempt to
>> minimize this problem.
> 
> Some time ago, while refurbishing a couple of SRR-13s, I ran across an 
> RCA-designed replacement for its ballast tube. I had never seen one before, 
> and was really intrigued by it. 
> 
> It consists of two back-to-back zener diodes, arranged/biased so that the 
> output is a modified-sine-wave. It outputs 6.3 VAC RMS using an 
> approximately 14 VAC RMS input. Input voltage can vary a lot more for this 
> circuit with no change in output, than the old tube-type ballast tube could 
> handle. But there is less heat produced, and it is far more reliable.
> 
> What it essentially does is to keep the peak of the sine-wave constant no 
> matter what the input does.
> 
> Receiver input-voltage fluctuations and their effect on the HFO or the BFO 
> tube's filaments are thereby pretty much eliminated.
> 
> The circuit is very simple, requires very few parts, and works extremely well.
> 
> I intend to use this circuit in those of my receivers which need it when I finish 
> restoring them.
> 
> I have seen other attempts to replace the ballast-tubes with solid-state 
> circuits for other receivers. Most of those are, to my mind, much too 
> complicated.
> 
> I will be happy to send a PDF of the schematic to anyone who asks for it.
> 
> Ken W7EKB
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