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Hackernap transistors and voltage rating, BC546 60v FE rails

Grog

Grog

pfm Member
about to finally put together a hackernap amp... better late than never!
I have 44-0-44v FE transformer (12V) and 32v-0-32v 300va output stage transformers (from the spares box)
currently planning to use 1M for R30/R34 etc, but not sure if the FE rail will be a bit higher than ideal given my output stage rail will be 43~~44v ish.
I guess reducing R30/34 and monitoring fet temps would be the easy way.

also been reading up about voltage rating of the small signal transistors, and wonder if BC546 are ok at these voltages, won't they see potentially rail to rail voltage in use?

did anyone have good experience for alternatives TR1,2,3,5,6
 
Thanks Pete, I see just 1 in stock though.
Has anyone tried MPSA06 in this position?
Also seen 2n3700 available, not sure if this would work well?
 
Lots of 2sa2547 on eBay some might be genuine, not.

I haven’t tried the 2n3700 but it’s high enough voltage it’s worth a try.

Pete
 
The hackernap has a front end filter so the IRF610/IRF9610 mosfet drops out around 8V, so you end up with 54v with a 44-0-44 transformer
The BC546 has a max voltage of 65V so I don't see a problem TBH

Have you read the thread in the ref section
Building a HackerNAP | pink fish media

Alan
 
Yes been through that thread.
I read somewhere that almost rail to rail voltage swings could be seen across the bc546, so ideally should be at least 100v rated.
Not sure how likely this is to happen in use, but as I'm building now its an easy change.
 
I read somewhere that almost rail to rail voltage swings could be seen across the bc546
Click to expand...

I understand your concern, but all the Hackernap amps in the initial Group buy and all NCC 200, 220 300 amps use the same BC465 and where the front end was supplied separately they all have a filter or reg in place to drop the voltage down.
I also don't remember any trend of failures for TR12&3.
If you wish to go for a higher voltage then that's fine.
Rail voltage after rectification and smoothing of 44VAC would be 62VDC and less than 15mA.

Alan
 
Thanks Alan,
Yes I guess this has been well validated by all the built amps.

I'm cracking on with the build now.
Sadly all my film caps 2u2 or larger are too physically big for c5-c11
I'll need to order some.

Is a single turn pot ok for bias, I usually go for multi turn but have already have some 2k 1T. Not sure how much adjustment range there is and how sensitive to adjustment this one is.
 
Single turn pots are fine just a bit tricky to set. But if you ordering some caps you could add them to the order.


Pete
 
ended up ordering, i was kind of keen to finish it off over the weekend, but gave up,
ordered some 25T pots, 3.3uf PP caps I hope to shoehorn in instead of the 2u2 PET's
I have 56uf film for C2 on one amp, and the second one I plan to build I've got 90uf film.
Thinking of going straight to the doubled up output transistors
 
Grog said:
ended up ordering, i was kind of keen to finish it off over the weekend, but gave up,
ordered some 25T pots, 3.3uf PP caps I hope to shoehorn in instead of the 2u2 PET's
I have 56uf film for C2 on one amp, and the second one I plan to build I've got 90uf film.
Thinking of going straight to the doubled up output transistors
Click to expand...
Parallel output transistor are a big leap forwards in sound quality, mine sound wonderful into arcs.


Pete
 
I keep hearing about wet tant's I should really try and pick a pair up to try,

everything about the parallel op TR's is good, so it makes sense to put them in from the start,
intrigued to know how the emitter resistor value may affect it, running 0R22 or 0R33 for each transistor,
I think 0R33 is the default, so will start here at least.
 
I use 0R33 for parellel output transistors it helps with current sharing agross the transistors, and as there are both in parellel its effectively 0R11.

I use 1R metal film resistors to make up the emitter resistors, they sound good and blow very fast under fault conditions, as I have found out.

Pete
 
good idea about the 1R metal films, i've got currently got 4w wirewound, I like the idea to parallel 1R MF resistors to give some failsafe
 
337alant said:
I understand your concern, but all the Hackernap amps in the initial Group buy and all NCC 200, 220 300 amps use the same BC465 and where the front end was supplied separately they all have a filter or reg in place to drop the voltage down.
I also don't remember any trend of failures for TR12&3.
If you wish to go for a higher voltage then that's fine.....
Alan
Click to expand...
The penalty for higher voltage rating is always lower gain and lower Ft
 
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