"Peter Hoon" <[EMAIL PROTECTED]> made an utterence to the drakelist gang ---------------------------------------------------------------------- Thanks to all the fellows who gave me advice.
Will address some of the comments below. Ron Wagner: Tks for your heads up on a "gentle tune up" for the twins. Am eagerly anticipating getting a copy soon. Agree fan is essential. Ron/WB4HFN: Not worried about my T4XC loosing value. Needs repair/alignment and corrosion removal on top chassis. Cost me $115. Figure that in early 1970 dollars, that is about $50 to $60. For a good one, maybe $110 in 1970 dollars. Once converted, repaired/restored and mated to a Sherwood Eng modified R4C, I think its value will hold at my $115 purchase price. So, we disagree that a convert will make the bottom fall out of its value, since it has already reached the "bottom"! Plan to use the C line twins as main station rigs for many years (rigs with solid state finals/front-ends get destroyed by static at this 9,000 foot mtn ridge QTH 5 miles from the continental divide). K6ZLP, Michael Felack and Al Parker: Tks for locating K5DKZ's detailed write up with picts on the mod, and the schematic. Our experience so far with T4X tune up: Decided to practice the tune up on all bands with a T4X in good op cndx that has used 6JB6 finals, expecting to "sacrifice" them to the learning curve. The first thing we noticed was how hot the convection air was coming from the RF cage (cover was off). Compared to our former Kenwood 830S, which had a potent fan near the final cage with 6146Bs, these tubes are substantially overheating during tune up, even when using a CW key to keep "on" periods very short. And they stay hot during normal CW ops, with plates glowing red in the dark. Why all this heat? Looked up 1963-1964 RCA specs for the 6JB6s, 6JB6As and the 6146As and Bs. In the case of the 6JB6s (6JB6A specs similar), we note that K5DKZ over-estimated typ op rating for a 6JB6 pair. The typical op class A1 rating, each tube, is for 17.5 watts of input power at about 16 Khz (audio). At higher HF RF freqs, this could be 30 to 40% lower, but let's assume at HF AB1 SSB service, the RCA max input rating of 17.5 watts. That means that estimated typ op input power for a 6JB6(A) pair in class AB1 (SSB) is 35 watts, compared to typ op AB1 (SSB) input power for a 6146A pair at 165 watts (6146B pair is 187 watts). And we're running the 6JB6s in the twins at 140 to 195 watts input power SSB on various bands, no fan? There is an enormous rated input power difference, around 470% for 6146As compared to 6JB6s in typ op class AB1 service! About 530% for 6146Bs. Visual comparison of a 6146A(B) vs 6JB6(A) shows a thicker plate, much larger plate surface area, and metal encased base (for heat dissipation), which confirms these data. (For comparison, another TV deflection tube, the 6DQ6A has a typ op rated input of 19 watts. McCoy runs this tube a little hot at 35 watts input in a 1965 QST CW Novice transmitter, equivalent to 70 watts for a pair.) To say that Drake is "pushing" the 6JB6s in the twins, with no fan, is an understatement. The tubes are mis-engineered for transmit service in the Drake twins. They are still mis-engineered even with an RF cage convection fan. Why would Drake, who otherwise has designed a fine transmitter (T4X, B, C), have chosen TV deflection tubes in the finals, vastly under-rated for their service requirements, with no convection fan, when an Xmit service tube, the 6146 in its various forms, has been available since 1952? Beats me. Since we want reliable service on CW and SSB emergency Forest Fire fighting nets here, with a tube that is still being manufactured, we will convert to 6146As, Bs or Ws, and add a fan in the next several months. Will post all details at that time. 73s and tks to all who contributed to this thread. Peter VE1CHS Nederland, Colorado ---------------------------------------------------------------------- On Behalf of "Peter Hoon" <[EMAIL PROTECTED]> Submissions: [EMAIL PROTECTED] Unsubscribe: [EMAIL PROTECTED] - unsubscribe drakelist in body Hopelessly Lost: [EMAIL PROTECTED] - help in body of message Zerobeat Web Page: http://www.zerobeat.net Brought to you courtesy of TLCHost.net http://www.tlchost.net/ ----------------------------------------------------------------------
