Available XPL909's and RCA410's

wattsabundant

wattsabundant

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An individual contacted me who was cleaning out his garage. Decades ago he worked in pro sound and used a ton of 400's. He has/had about 75 XPL909's and 20 or more RCA410's/66546 and a smattering of some other transistors, all small quantities. After a few emails I realized he had been a customer of the pro sound company I worked at.

Anyhow, if someone has a sincere interest let me know. For all I know they may be up on EBAY now.
 
I don't think the XPL909's are worth much, as we typically replace them with the current ON Semiconductor MJ21196G NPN output transistors. But the RCA 410 and 66546 driver transistors could have some value to those of us building quasi-complementary WOA amps for folks that cannot afford the full complementary treatment.

I would like to get a set of four or eight just to see if I could get some better matches with the ones I currently have that seem to be all over the place with their hFE (beta) values.

Thanks,
Mark
 
I am also in need of some 66546’s to restore my amp to more or less original condition. What could you spare and how much, please ?
 
If the amp is quasi comp you only have to have the 66546 in the negative leg of each channel. The positive leg can use an XPL 909 or TP9054/MJ15024 etc.
 
I received 12 of the RCA 66546 driver transistors from the individual who contacted wattsabundant. I understand they are 'better' than the RCA 410 driver transistors; but I have not researched why. They do seem to have a bit more gain (between 40-60) and the hFE numbers are more consistent, at least in the group I have.
 
mlucitt said:
I received 12 of the RCA 66546 driver transistors from the individual who contacted wattsabundant. I understand they are 'better' than the RCA 410 driver transistors; but I have not researched why. They do seem to have a bit more gain (between 40-60) and the hFE numbers are more consistent, at least in the group I have.
Click to expand...

Hi Mark
Did someone make that claim that those are better?
 
Gepetto said:
Hi Mark
Did someone make that claim that those are better?
Click to expand...

I have a sticky above my bench with the RCA 410/66546 parameters and next to 66546 it says "better". I wrote that several years ago, I cannot recall why, so I did some research, some of it rings a memory cell or two..., some is contradictory.

From AudioKarma link to the old phasetek site (Ed would know about this)
"RCA 410 vs. RCA 66546
Both are selected RCA 410's (see data sheet). The selecting was done to improve reliability of the Model 200/200B amp. The 66546 had a slightly larger die and the 66430 had a slightly higher Ft. Both can be used interchangeably with the 410 as drivers in quasi-comp 400s and 700s."
See attachment

Phase Linear Service Bulletin 1-80:
"66546 (RCA) - This is our own number stamped on RCA 410 devices which may be available locally."
See attachment

From - https://oldtube.com/Oldtube-semiconductors.htm
"(# 66546 is renamed RCA410, and had been used in some old Phase linear amplifiers)"

Joe, do you have an opinion on the RCA 66546 as driver transistors?
 

Attachments

Hi Mark
Only opinion is what is posted in your post, that the RCA410 and 66546 are technically the same, the latter private branded and in some cases produced by a different supplier (Moto vs RCA).

The lower the gain bandwidth the better. PL struggled with stability in the quasi construct (2nd and 4th purple heatsink phenomenon)
 
Gepetto said:
Hi Mark
Only opinion is what is posted in your post, that the RCA410 and 66546 are technically the same, the latter private branded and in some cases produced by a different supplier (Moto vs RCA).

The lower the gain bandwidth the better. PL struggled with stability in the quasi construct (2nd and 4th purple heatsink phenomenon)
Click to expand...
Gain bandwidth? This is a new term to me, I know about gain or 'amplification factor' (hFE) hybrid, forward transfer characteristic, and common emitter configuration. For example: if 1mA is fed into the base of a transistor and it has a hFE of 100, the collector current will be 100mA.

I also know about bandwidth (Ft) transition frequency to unity gain and (Fmax) which I believe for the RCA 410 is 2 MHz. Is this high enough for a 20-20KHz amplifier? Is there a rule of thumb for this? Transistors with Ft of up to 50 MHz become very expensive, is this needed for drivers? Is self-oscillation a problem here, do we need base stopper resistors? These are the questions that keep me awake at night...

How do we determine gain bandwidth at our level? Is it something we can control or select?

And can you explain the 2nd and 4th purple heatsink phenomenon, I don't know what that means. Thanks!
 
I believe the 2nd and 4th heatsink is the negative DC leg for each channel. In quasi comp systems it is critical that the RCA 410 is used, as opposed to an MJ15024/21196 to prevent oscillations. I learned the hard way that using the same transistor for driver and outputs leads to oscillations. I stare at the schematic and struggle to understand why. I spent hours trying slow down tricks, base stoppers etc and nothing worked.
 
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