The Citation 16A resurrection project

[PB2]

Yeah, that's fine, if you have hands on experience then go for it. I was just being cautious.

I only just took a closer look at the output stage, didn't notice earlier that it is Quasi-complementary and uses RCA outputs.

It's older than I originally estimated so the input transistors would more likely be 2n5210 and the complement. I suggest you try to find out what the correct devices were and if they were matched.

It's fine if you want an authentic restoration, go ahead enjoy!

Pete B.

[taj]

Hi Pete,

You meant RCA inputs I hope. It uses normal binding posts for outputs. Yes, it's a QC output section with TO-3 drivers sharing space on the heatsinks.

Oh wait. You mean RCA output devices. Doh. I'm a little slow. Okay a lot slow.

You're absolutely right. I should find out what the original input section transistors were, and go from there. I've been searching and looking but I can't find that information.

Does anyone with a Cit. 16 know? Are the devices marked?

Thanks,

..Todd

[taj]

Originally posted by taj
They certainly aren't at Pass or Kress level, but they are a well-respected classic amp

I just noticed this typo. I'd like to build a Kress one day. Designed by the legendary Palsen Kress no doubt.

..Todd (slow I tell yah)

[EchoWars]

Does anyone with a Cit. 16 know? Are the devices marked?

I have some...somewhere. IIRC the numbers on them did not correspond to any RCA part that I'd ever heard of.

The blown Cit16 that I rebuilt a long while back got MJ15003's and MJ15004's for driver duties and outputs.

[taj]

Hi EchoWars,

I'm not so sure you used the 15004s unless you de-Quasi'ed the output section.

I also recall DJK recommend using 15024s I think. So the output section isn't a problem to re-construct. The input section has me a bit frustrated though.

It looks to me the like the input section transistors need to be rated about 30v/30mA, but other than that I don't know what I'd be looking for. Can anyone tell me which parameters would be significant when trying to match a device to a circuit (in this case the current mirrors and the diff. amp)?

BC550/560 look good to me based on electrical tolerance and noise.

..Todd

[EchoWars]

Originally posted by taj
Hi EchoWars,

I'm not so sure you used the 15004s unless you de-Quasi'ed the output section.

My bad...just used to listing both NPN and PNP.

I also recall DJK recommend using 15024s I think. So the output section isn't a problem to re-construct.

No indeed. There's lots of suitable transistors for the output.

The input section has me a bit frustrated though.

It looks to me the like the input section transistors need to be rated about 30v/30mA, but other than that I don't know what I'd be looking for. Can anyone tell me which parameters would be significant when trying to match a device to a circuit (in this case the current mirrors and the diff. amp)?

BC550/560 look good to me based on electrical tolerance and noise.

..Todd

Looks like an LS313 would do for the dual NPN input, but since the board has all six pads available, you can match your own.

What you decide in is really a matter of preference, as there are tons of devices that would do the job well. I would not get to hung up on noise specs. Since it 'appears' that the small signal devices are all EBC layout, the BC parts might be a good way to go. Zetex transistors, which I am fond of, are also EBC layout, so that's another possibility...using something like ZTX694B and ZTX795A. I'd match a couple of ZTX694B's with gains over 1000 for the input pairs and the Q8 current source, and use the BC devices for the rest.

Is there something funky with the input impedance that I don't see that makes the use of a huge 100µf input cap necessary?

[PB2]

If you like Krell, the KSA-50 is a simpler design than this HK, and could be scaled up for voltage/power:
http://www.diyaudio.com/forums/showt...398#post490398

The builders here may have already done this, have not read the thread carefully. I'd reduce the output bias to perhaps 20W/ch at idle.

Not saying that this is the best design, just better than the HK.

Pete B.

[taj]

Originally posted by EchoWars
Zetex transistors, which I am fond of, ...

That's great info. I've steered clear of Zetex just because of unfamiliarity, and a general lack of mention in these forums. So your suggestions will probably be of interest to a few others as well (assuming others read this).

Just curious, why is high hFE important for the diff amp?

..Todd

[Original Burnedfingers]

I also recall DJK recommend using 15024s I think. So the output section isn't a problem to re-construct. The input section has me a bit frustrated though.

Use the MJ15024's like DJK suggested.

And for the input differential pair (a nameless dual NPN job), will a pair of matched, thermally coupled 2SC2240's be adequate? They are low noise, linear...

Just match a pair of 2n5551's for the front end.

[EchoWars]

Just curious, why is high hFE important for the diff amp?

The higher the gain of the input pair, the better. This sets the input impedance of the amp, and the 'inner' transistor accepts the feedback from the amp output. Sloppiness here from low hfe will show in the final product.

Zetex makes a lot of transistors which are quite nice for audio use...I use a lot of the ZTX694B, ZTX795A, and the ZTX1056A.