From: Garey Barrell 
Subject: Re: [drakelist] R-4B problem around V8 mixer


Garey Barrell  made an utterence to the drakelist gang
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Mike -

Unfortunately, I think you have made the correct diagnosis of a "fried" 
T3.  

I had a similar occurrence a few years ago with T?.  First symptom was a 
crispy 1.5k resistor.   The failure was a short internally in the T? 
assembly.   It was the transformer with the external ferrite, and the 
transformer posts were cut off on the inside end with side-cutters vs 
flush cutters, leaving a knife edge end.  There was a rubber pad between 
the bottom of the ferrite and the end of the posts, but after "only" 30 
years the sharp edge cut through the rubber pad and shorted to the 
ferrite. 

OF COURSE the post that punched through first was on the end of the 
transformer winding end  _away_  from the B+, melting the coil 
insulation and destroying the transformer.  Drake had no more 
transformers, but did have just the core with winding and I was able to 
repair it that way.   I have since checked three other similar units, 
and in each case the transformer posts were bent over before being cut 
off, eliminating the problem. 

Good luck finding a replacement.  Maybe Bill Frost has one in his "junk" 
drawer!?!?

73, Garey - K4OAH
Atlanta

wa3wom{at}comcast.net wrote:

> Hi group,
>
> I was a very bad boy!!  I enjoy building and testing solid-state tube 
> replacements for the Drake R-4B just for fun but I screwed 
> up. I carelessly plugged a new (including solder short) version of the 
> SS-AU6 for the Collins S-Line into the socket for V8 - the 6HS6 mixer 
> and smoked R51, the 150 ohm resistor, while I was testing a bunch of 
>  newly built SS-HS6's. I test-tacked a new resistor into the circuit 
> and replaced all of the SS-tubes with real vacuum tubes known to be 
> good but still have low sensitivity and can't find anything else 
> obviously wrong.
>
> I checked with the big guns of Drake repair and they are backed up for 
> a good while with prior repairs so I figured to try more 
> troubleshooting myself while waiting for an opening to send it out.
>
> Any ideas on what else I can check?
>
> My fear is that in order to smoke R51, I may have also have smoked the 
> insulation on the windings in T-3, changing it's value and function.
>
> In that event, does anyone have an R-4B T-3 available in their spare 
> parts bin?
>
> Oh well, live and learn. It's been 20 years since I regularly worked 
> on Drake 4-Line equipment and my skills have become quite "tarnished" 
> in the interim, sort of like a B-Line copper chassis. ;-)
>
> TNX ES 73 DE MIKE WA3WOM K
>

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