[TechAssist] Re: FYI 2SC4834 Sony power supply transistors Q601,Q602

  • From: "becyn" <becyn@xxxxxxxxxx>
  • To: <techassist@xxxxxxxxxxxxx>
  • Date: Fri, 7 Nov 2003 20:46:46 -0500

We have NEVER used matched pairs in power supply, just the same lot numbers
.
It is very important to change the three vdrs and the resistor.
This has been a ZERO FAILURE strategy for us.
What will kill the supply is failing to resolder the H drive transformer and
changing the H out (which caused the problem in the first place).

The higher gain transistors will run cooler due to a faster di/dt
transition. I don't think it's worth all the effort though.
Time is money!

Jim McVey
McVey Alltronix
327 Broadway
Newburgh Ny 12550
ph: 845 561 8383
fx: 845 561 9017
Consumer electronics &
computer service.
Factory authorized for
over twenty brands.
----- Original Message ----- 
From: "Tel-Tek Electronics" <teltek3@xxxxxxxxxxxx>
To: <techassist@xxxxxxxxxxxxx>
Sent: Friday, November 07, 2003 6:45 PM
Subject: [TechAssist] Re: FYI 2SC4834 Sony power supply transistors
Q601,Q602


> Would almost call for a "matched pair", since this duty cycle is so
> critical.
> I'm getting the Sony kit from Global, and I doubt they are trying to
> match them up, even though it's suppose to be a kit.
> Just had one of those sets a couple of days ago...very important to
> change those VDR's. VDR601 and VDR602.
> BTW...that Sony-SPKIT sells at Global for $9.95..which includes the 601
> and 602...the H/O transistor and a .1 ohm resistor. That $9.95 Can.
> Which is probably about $7 US.
>
> -Ed-
>
> Ed Gaidies
> Tel-Tek Electronics
> Ontario-Canada
>
> teltek3@xxxxxxxxxxxx
>
> -----Original Message-----
> From: techassist-bounce@xxxxxxxxxxxxx
> [mailto:techassist-bounce@xxxxxxxxxxxxx] On Behalf Of Leonard G.
> Caillouet
> Sent: Friday, November 07, 2003 6:01 PM
> To: techassist@xxxxxxxxxxxxx
> Subject: [TechAssist] FYI 2SC4834 Sony power supply transistors
> Q601,Q602
>
> Just a few notes on these transistors and the results of some
> experimenting.
> I had a KV27ts32 and a KV32s25 in the shop with the classic HOT shorted
> and
> Q601,602 shorted.  I had some 2SC4834M in stock and ordered some plain
> 2SC4834 from Tritronics and some 2SC4834P from Acme Enterprises
> (Orlando).
> I tried each type in both sets and found that the higher rank (letter)
> transistors ran progressively cooler.  I matched the transistors from
> batches of 10 by forward bias voltage on the junctions then in circuit
> for
> nearest to 50% duty cylce.  I have found that swapping pairs or swapping
> the
> caps on Q601,602 can often improve the ratio to closer to 50%.
>
> Interestingly, the higher gain transistors ran cooler by 10-20 degrees,
> depending on the set, but the overall current drawn by the set was
> virtually
> the same(~60-70 mA with & without a signal)
>
> Summing up, it appears that the higher rank transistors are the better
> choice.  Acme has them at a great price(10 for $15.95) and has free
> shipping
> for the time being on orders over $25.  They are a new operation but
> Glen,
> the main contact there was a manager for MCM at one time and seems
> veryinterested in winning over the business of shops like us.  So far
> they
> seem to be good to work with.
>
> BTW, the KV32S25 was a bit atypical in that the HOT failure was due to a
> bad
> FBT.  The price was pretty steep and the customer did not want to fix
> it, so
> I gambled and tried an aftermarket transformer from HR.  It seems fine
> so
> far and at the lower price the customer went for the fix.  We'll see if
> it
> holds up.  I don't like subbing flybacks but these have had a good rep.
>
> Leonard G. Caillouet
> Electronics World
> Gainesville, FL
> 352-332-5608
> 352-332-5668 (fax)
>
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