Thunderbolt Discussion

[Brian Carling]

The guy looking for this help is on the eham.net
forum known as "Boatanchors."

I don't own a Thunderbolt these days.

On 19 Jan 2005 at 9:14, George Maier wrote:

> In addition to the areas you mentioned, Brian, the primary areas of
> suspicion would be:
> SW105 (HV interlock switch)
> C8 (HV bypass cap)
> C19 & C20 (plate blockers)
> 
> After that, it's an Ohm meter exercise on HV buss.
> 
> Cheers,
> George - K1GXT
> 
> -----Original Message-----
> From: Boat Anchor Owners and Collectors List
> [mailto:BOATANCHORS at LISTSERV.TEMPE.GOV] On Behalf Of Brian Carling
> Sent: Wednesday, January 19, 2005 7:50 AM
> To: BOATANCHORS at LISTSERV.TEMPE.GOV
> Subject: [BOATANCHORS-TEMPE] Thunderbolt Discussion
> 
> I thought this exchange might interest you guys...
> 
> N5RVZ wrote:
> have restored this amp and the only problem is the HV pops a 
> fuse every time the HV Plate switch is thrown. 
> 
> I have replace the following. 
> (1) Original 866's with solid state 
> (2) HV Cap's with new ones 
> (3) New HV wiring underneath, from HV caps to 4-400's 
> (4) Replaced existing 4-400's with other sets 
> (5) Got HV Plate transformer rewound 
> 
> I am at a loss what is still the problem! When I disconnect the 
> HV at the caps from the rest of circuit. I have AC HV at the 
> end of HV section transformer Coil L101. Doesn't blow the 
> fuses at this point. Something is shorted after this point! 
> 
> Can anybody help? 
> 
> Thanks in advance. 
> 
> Keith - N5RVZ 
> = = =
> Keith - you should eliminate one thing at a time. 
> 
> STEP #1 - 
> Try disconnecting the rectifier from the HV 
> secondary of pyour plate transformer. Does it 
> blow the fuse now? 
> 
> If so, then your transformer is bad or your wiring is wrong. 
> Check all wiring for shorts. 
> Use an ohm meter to mneasure the resistance of your 
> transformer windings. Use the LOWEST ohms range. 
> They should be something ABOVE zero ohms, even if they are 
> only an ohm or two. 
> 
> STEP #2 - 
> If it all looks OK up to that point, you should 
> try connecting JUST the rectifiers (no caps or load.) 
> Does it blow the fuse now? If so, then you might 
> have some shorted out rectifiers. This could have occurred 
> because a) They were bad to begin with. OR 
> b) Because the inrush current to the capacitor(s) 
> is too much for them. You nee dto limit the inrush current, 
> because the original circuit had tube 
> rectifiers that allow a bit of E/R current limitation 
> through the 866As. 
> 
> Let us know how you are progressing after the above two 
> steps. Consider adding some resistors in series 
> with your rectifiers. I have never done this but 
> I hear that some guys add like about 10 ohms at 20 
> watts to ease things up for the circuit. Remember, 
> with today's higher line voltage AND the higher plate voltage 
> you get from the sand state rectifiers, you have probably 
> increased the plate voltage by 10 to 20% over what it was in 
> the original application! 
> 
> Brian, AF4K
> FROM AF4K:
> 
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