[Heathkit] HO-10 Monitor Scope transformer

[Robert & Linda McGraw (K4TAX)]

An off the shelf transformer might work just fine.  Keep in mind that the 
heater of the CRT is some 1300 volts above chassis/ground.  Thus any off the 
shelf transformer will need two 6.3 volt windings.  One for the CRT heater 
and one for the rest of the tubes.  If you should find one with 2500 volt 
test insulation on the 6.3VAC winding consider yourself in luck.  The 
standard insulation of 1500 volts is a bit iffy.  You'll also need a 2nd 
secondary to produce about 600 volts via a voltage tripler scheme and also 
pick off 215 volts for the sweep generator.

Typical supply voltages are:
-1430VDC with positive chassis/ground
+600VDC with neg chassis/ground
+250VDC with neg chassis/ground
6.3VAC for the CRT
6.3VAC for the other tube heaters

The original transformer had 4 windings of the following voltage
600VAC doubles to ~1430 VDC
215VAC triples to ~600 VDC and 1/2 wave rectified to 250VDC
6.3VAC for the CRT heater
6.3VAC for the heaters

 A word to the wise.  If you haven't changed the 0.15 MFD 1600V volt caps in 
the HV section, DO SO now.  It may save your transformer.  Mouser has 
HiVoltage Metalized Polypropylene Film Capacitors for about $5 each.  Their 
part number is 5984-940C16P15K-F

73
Bob, K4TAX

----- Original Message ----- 
From: "Peter Markavage" <manualman at juno.com>
To: <Heathkit at mailman.qth.net>
Sent: Thursday, April 05, 2007 11:49 AM
Subject: Re: [Heathkit] HO-10 Monitor Scope transformer


> There was an article in Electric Radio, Nov. 2003, page 28, on the
> modification of the HO-10 using, I believe, several off the shelf type
> transformers. Don't have the issue handy to look. You might also consider
> one of those AC or DC input, HV cube/potted supplies (high voltage/low
> current).
>
> Pete, wa2cwa
>
> On Thu, 5 Apr 2007 10:40:34 -0400 "Tom Chesek" <tchesek at epix.net> writes:
>> As suspected the transformer in my HO-10 monitor scope is bad. The
>> high voltage winding is open. There is no short to ground at this
>> point but if I apply power it heats up and starts to smell,
>> therefore I assume if I left it powered on it would eventually cook
>> off all of the insulation and short to ground. I am not interested
>> in spending a lot of money to have the transformer rewound.
>> Physically this scope is very nice, so I want to fix and use it
>> myself.
>>
>> I know it is asking for unobtainium but does anyone have an HO-10 or
>> HO-13 transformer that you are willing to part with? Second choice
>> would be a SB-610 or SB-620 transformer. If not I will have to
>> proceed with fabricating an external supply. Is anyone else running
>> one of these scopes with an external supply and if so what is your
>> configuration?
>>
>> 73,
>> Tom K3TVC
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