Hell-marriage amp (5842-> IT -> 2A3)

[pre65]

How have you wired the interstages ? (what colour goes where)

Here ya go Phil, like this.



and...



DTB

Going by the Hammond web site diagram that looks right.

[Mike H]

@ our-Phil. Re-Grid leak R's across the IT, Oooer, no I haven't notice that before TBH. I suppose if the resistance of the winding was higher than the spec'd max grid leak resistance i could see that being a reason but these are low, DCR is 175R.

I'd have thought the treble would be peaky if it were that fussy about that.

Mine have only got the resistors as like a "safety feature" if the IT sec.s should go OC for some reason. Like I didn't solder it on properly

Having said that though, they do give the driver valve what looks like a 390k load (plus capacitances) for most of the frequency spectrum. By which I mean you can control its gain like that.

The acid test is drive the 2A3's with something else - anything else - if all is hunky dory, then it's not them.

What's the input coming from? It's not a Miller cap issue again is it? Duno what the gain of the 5842 is but could be high cos of the inductor load.



 

[Mike H]

I think Mike does on his Aurora version 926,142,831 (f) revised.

version 926,142,832 ¾

..... revision 11 and seven eighths



 

[Mike H]

Dave you got a sig gen? You can try scoping the driver anode and the IT sec separately, see if the HF response falls off the same on each, or differently, or whatever



 

[pre65]

I think Mike does on his Aurora version 926,142,831 (f) revised.

version 926,142,832 ¾

..... revision 11 and seven eighths

If you get a small improvement at every revision it must, by now, be perfik.

[Mike H]

Not far off! Meh it'll do



 

[thomas]

You pleased with your breadboard Thomas? First time you played with IT's too I'm guessing?What IT you playing with our-Thomas? Danburys?

Absolutely delighted with mine, primarily as they didn't go 'bang' when I switched them on but also they've sounded excellent... Txs were Danbury's finest...Wired up as per Mike's instructions but basically as you have wired up yours....I didn't use fixed bias, admittedly (too complicated for me!). I wonder you could certainly drop in a D3a driver there?!

As regards 8k instead of 33k R - does seem a little out of spec- but if that gets -45v...?!

[pre65]

I wonder you could certainly drop in a D3a driver there?!

Your D3a will be with you Tuesday.

[thomas]

What is upfront of them? I'm using a 47K HK stepped pot- I read somewhere that a 100K pot will cause treble roll off....

[Mike H]

i did have to sub in a 8K2 instead of the spec'd 47K/33K in the fixed bias network to get the required -45 volt on the bias pot range

Ah!! You sure the adjacent 22uF's are connected to ground, not just the bottom ends of the pots?

JTS (who described in 2 words consisting of 'crap'

 

[Nick]

My money is on the interstages needing swapping. The inter-winding capacitance especially if they are bifilar wound works as a big ol cap to ground on the output.

Failing that, as someone said, use your scope and a signal source and see where the HF goes away.

[pre65]

My money is on the interstages needing swapping. The inter-winding capacitance especially if they are bifilar wound works as a big ol cap to ground on the output.

Seems perverse that, use them instead of a coupling cap and end up with capacitance problems.

[Nick]

There is always inductance, capacitance and resistance, as much as we might like to assume things are ideal.

[Will]

Dave..sounds like the I/T is not up to it..SJS or SP wound do a guden..

The 5842's problem is its size.. too small it gets very hot gets noisey and dies..6c45p is better.

Fixed bias I dont like the sound .. solid state.. electronic..

I dont like the 2A3 but thats me..

dht.it.dht.it.dht

.

[Andrew]

dht.it.dht.it.dht

Is that a footy chant?

I'd say ITX the wrong way around too.

Andrew