"n0tu/Steve" <[EMAIL PROTECTED]> made an utterance to the drakelist gang ---------------------------------------------------------------------- Thanks Garey! Sounds like that bias supply is the Achilles heel of the Drake PSs!
2007/12/13 Peter Bent <[EMAIL PROTECTED]>: > > "Peter Bent" <[EMAIL PROTECTED]> made an utterance to the drakelist gang > ---------------------------------------------------------------------- > Thanks Mike, > Good warning... I had no idea.. I'm going to order the kit. > > > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On > Behalf Of Garey Barrell > Sent: Thursday, December 13, 2007 2:46 PM > To: [EMAIL PROTECTED] > Subject: Re: [drakelist] AC3 VS AC4 > > > Garey Barrell <[EMAIL PROTECTED]> made an utterance to the drakelist gang > ---------------------------------------------------------------------- > Alan - > > The AC-3, (with the exception of a very few early units,) is > functionally identical with the AC-4. > > The fault that makes an AC-3 "cook a set of finals" is exactly the same > fault that can cause an AC-4 to do the same! This "fault" is a failure > of the bias portion of the power supply, which is identical in both > supplies. The bias supply is by far the most "critical" part of the > AC-3/4. It is used to keep the T/R relay in the standby condition, and > limits the idle current drawn by the final tubes in transmit, among > other things. > > The failure mode is this..... One or both of the filter capacitors in > the bias supply of the AC-3/4 dries out. The "early warning", if you're > lucky, is erratic VOX operation, the VOX taking longer to drop out than > it should, or increasing idle current in the final. If you're NOT > lucky, like most of us, one of the filter caps will short, killing the > bias supply completely. Even if the transmitter is in standby, while > you have gone to the kitchen for a snack, or to a hamfest, when the bias > supply fails the T-R relay will close, putting the transmitter in > transmit. Since there is no bias, the final tubes will draw as much > current as they can until either one of the final tubes melts, shorting > the HV supply, and hopefully blowing the power supply fuse, (assuming > you or a previous owner hasn't replaced it with a piece of #000 copper > wire,) or burning up the transmitter, power supply and/or house! > Alarmist? Yeah..... You wanna take the chance? Didn't think so....... > > At the very least, with a "new" or unknown, or even a supply you've had > "for years", replace the filter caps on the bias supply NOW if they > haven't already been replaced within the last 10 years. Better yet, > upgrade your AC-3/4 with the AC-4R kit from Mike at The Heathkit Shop, > and forget about it for another 30 years or so. Also, check that the > fuse is either 5 or 6A Slo-Blo. Early supplies are marked 5A, but > tended to blow from the turn-on surge and so was increased to 6A. > > Finally, (at last,) the answer to your question.... Yes, the supplies > are fully interchangeable across the 4 Line. The AC-3 doesn't have the > VOX connector to key a linear amplifier, since the AC-3 was for the TR-3 > and very few people wanted to put a linear behind a transmitter that put > out 200 W. The little RCA jack pigtail coming out of the back of the PS > connector was originally wired for the speaker with the TR-3 or TR-4. > If you need an external VOX jack, the easiest way is to add another RCA > pigtail in the Cinch connector. > > 73, Garey - K4OAH > Glen Allen, VA > > Drake 2-B, 4-B & C-Line Service Supplement CDs > <www.k4oah.com> > > > > [EMAIL PROTECTED] wrote: > > [EMAIL PROTECTED] made an utterance to the drakelist gang > > ---------------------------------------------------------------------- > > I was trying to find out if the AC3 power supply can be used with the T-4 > > > series transmitters or whether the AC4 is necessary. Searching the Drake > > archives I stumbled across one of the few postings addressing the > subject: > > ------------------------------------LIST > > POSTING--------------------------------------------- > > > >> Does anyone know if there is a differnce between the Drake AC-4 and > >> AC-3 power supplies electrical wise in the connector? I have both and > >> the AC-4 works fine but the AC-3 seemed to cause various problems > including > >> cooking a set of finals in a T4XB. Seems like it causes the T4XB and > T4XC > >> to go into transmit part of the time. > >> > > > ---------------------------------------------------------------------------- > -- > > ------------------------- > > I was hoping to get a clarification from this list. > > > > Thank you > > > > Alan KB7MBI > > > > > > > > ---------------------------------------------------------------------- > Submissions: [EMAIL PROTECTED] > Unsubscribe: [EMAIL PROTECTED] - unsubscribe drakelist in body > Hopelessly Lost: [EMAIL PROTECTED] - help in body of message > Zerobeat Web Page: www.zerobeat.net - sponsored by www.tlchost.net > ---------------------------------------------------------------------- > > > > ---------------------------------------------------------------------- > Submissions: [EMAIL PROTECTED] > Unsubscribe: [EMAIL PROTECTED] - unsubscribe drakelist in body > Hopelessly Lost: [EMAIL PROTECTED] - help in body of message > Zerobeat Web Page: www.zerobeat.net - sponsored by www.tlchost.net > ---------------------------------------------------------------------- > ---------------------------------------------------------------------- Submissions: [EMAIL PROTECTED] Unsubscribe: [EMAIL PROTECTED] - unsubscribe drakelist in body Hopelessly Lost: [EMAIL PROTECTED] - help in body of message Zerobeat Web Page: www.zerobeat.net - sponsored by www.tlchost.net ----------------------------------------------------------------------
