Asteroid with diode rectifier and 4.3k output

[deuce42]

Hi guys

I had decided to build a K50 amp but have now decided I'd rather make a k60. Something about a softer more chimey amp is where I'd like to go where as the K50 clips I've heard have more of a thicker marshall flavour which I'm guessing is the result of using the extra triode on the second tube and some other differing component values.

Unfortunately I've already got a 4.3k output transformer and my chassis doesn't have space for a GZ34 or the like, so my question is: - what would be the effect of building the asteroid layout but with a diode rectifier and a 4.3k output transformer rather than the asteroid's normal 5.8k and tube rectifier?

Thanks very much

[Roe]

the diode will sound a little punchier and harder. or it will be less compressed. the 4k3 may sound a little thicker and more powerful than 5k8. with slightly different overtones

[martin manning]

You could also simulate the vacuum rectifier's voltage drop by placing a resistor in series with each silicon diode, say about 100 ohms, 5 or 10W.

[deuce42]

You could also simulate the vacuum rectifier's voltage drop by placing a resistor in series with each silicon diode, say about 100 ohms, 5 or 10W.

So it would go HT-diode-100 ohm resistor- then next diode -100ohm resistor etc and repeat for each diode?

[martin manning]

Just one resistor per HT leg. Each of the two diodes shown below could be two or three in series. I'll revise the value of the resistors downward to 75 ohms, after looking up some previous work.

[deuce42]

That's so helpful thanks Martin.

[Roe]

some place the resistors after the diode. I like the wz68 with my k60. the resistance of it is probably just 30R

[deuce42]

Thanks Roe - I'll give the WZ68 a go then!

[deuce42]

And could I clarify another issue - I believe the choke used for Asteroid is a 10hy 200ma.

This is not an easy choke to find I realise. How low ma rating could I get away with the choke? I realise its about screen grids on the tubes but I'm confused with whether I need a 200ma choke or could get away with a lower rated one. Also wondering what difference a lower hy amount will make?

[M Fowler]

Call Heyboer and order a choke.

[pablogt]

The Heyboer choke for the K-50 (guess it's the same for K60) is hts-7750-1 10H/200ma

P.

[Roe]

yes, the choke is the same.

[deuce42]

thanks guys. Out of interest, why does the MA rating of the choke need to be so high? -ie 200ma? Wouldn't a twin EL34 amp with 3 preamp tubes need much less than this? Like less than half the MA capacity normally? I ask just for my own learning.

[rp]

I had to google wz68, thought it was a type of diode or something. This popped up and gives a clue what's inside one, if anyone cares. Didn't know it had a thermistor inside too, those things like to fail, or buzz. And 20K seems way high though the poster appears to know what he's doing.

http://dynacotubeaudio.forumotion.com/t ... copper-cap

I just re-built my Weber copper cap after it blew up. They are bonehead simple inside. The parts are all easy to find and consist of: 2 10 watt 20K wound resistors, 4-4007 diodes , 1 NTC 100D-11 thermistor for the delay. They are all on a little pc board that makes easy to do the replacement.

[rp]

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