Power Supply in a Concord

[deuce42]

Hi guys

I've built an Asteroid and want to turn it into a Komet 60 "HD" style mod. Ie diode rectifier and concord style power supply. I once had a copy of a K50 schematic but cannot find it anymore.

Can somebody tell me if the power supply filter caps are different from the K60? i.e. 220uf instead of 80uf for the caps between the choke? I have this recollection the power supplies are different and these cap values were the difference.

Thanks so much

[Mark]

See if this helps?

https://ampgarage.com/forum/viewtopic.p ... t&start=15

[deuce42]

Thanks Mark, I did read through that thread previously but couldn't ascertain whether the power supply was different, at least my recollection of the filter caps between the first and second notes being a different value.

Can anyone enlighten me if I'm missing something?

[deuce42]

I'm guessing from looking at the photographs there is a different "black" filter cap behind the 80uf sprague atom but can't read the value. Perhaps this is my answer - its enigmatic the 220uf?

[Roe]

replace the two 80uf caps at the mains with 220uf caps. replace the gz34 with ss rectifier

[deuce42]

Ha yep as I suspected. Thanks!

[deuce42]

I have one last question guys if you could help

The K50 has a 22k resister between the choke and the PI filter cap. The K60 has a 1k. Why the difference between the two in these two schemes?

Can anyone enlighten me?

[Roe]

the voltages of the concord are higher due to the ss rectifier

[deuce42]

ah of course I hadn't thought of that. Thanks

[Roe]

the concorde is also supposed to be closer to an express than what the k60 was. the express has much lower voltages and uses 18k2 between the screens and phase inverter. Perhaps they just though that 22k worked the best with this particular circuit. The question now is what the k60 HD uses

[Mark]

The Concorde has a cathode follower after the cold clipper, that is going to significantly alter the sound of the amp. By all accounts the Concorde is a rock amp.

[Roe]

the cathode follower is fairly subtle in this case. I've made mine switchable. but it does draw more current, lowering the preamp voltages somewhat

[Mark]

You'd want to be hitting the cathode follower pretty hard to cause compression and thicken up the sound of the amp. I wonder why put the cathode follower there if it only makes a subtle difference.

[Roe]

Yes this has been discussed previously. some say its a waste here. Even Aiken commented on this. However, I do hear a small difference. it does add some compression and warmth when you turn up the volume

[deuce42]

the concorde is also supposed to be closer to an express than what the k60 was. the express has much lower voltages and uses 18k2 between the screens and phase inverter. Perhaps they just though that 22k worked the best with this particular circuit. The question now is what the k60 HD uses

I know this is an old thread to dig up but can anyone enlighten me on the the K60HD's resistor value between screens and PI?

It seems the K50 uses a 22k and the k60 uses a 1k. As the "HD" version is supposed to be the power supply of a K50 with the preamp and power amp of a k60, I'm a bit confused. Presumably using a 22k would lower the plate voltages of the 12ax7's in the preamp and power amp. If the "HD" version is a still a K60, this would change the sound of the K60 I think unless I'm missing something? So I'm guessing the answer would be to retain the 1k to make it a K60 "HD"?