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Old 26th March 2009, 02:35 AM   #1
nhuwar is offline nhuwar  United States
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Default 304tl se amp

Does anyone have any schematics of some 304tl se amps?


Just looking for ideas?


Thanks,
Nick
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Old 26th March 2009, 07:13 AM   #2
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See here:
http://www.alumrocktech.com/amplifier.shtml

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Old 26th March 2009, 08:09 AM   #3
Gluca is offline Gluca  Italy
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Me! Me! Mine.

this is my 304TL amp

Rx sets the bias for the 304TL. You need two separate PSUs and, what else?, yes heating the tube is not an easy task.

Good luck with the OPT, not easy to find a good one.

Gianluca
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Old 26th March 2009, 09:21 AM   #4
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Quote:
Originally posted by Gluca
Me! Me! Mine.

this is my 304TL amp

Rx sets the bias for the 304TL. You need two separate PSUs and, what else?, yes heating the tube is not an easy task.

Good luck with the OPT, not easy to find a good one.

Gianluca
Ciao Gluca,

Why is the cathode of the 304TL and output transformer elevated to 330V?

Grazie,
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Old 26th March 2009, 10:41 AM   #5
Gluca is offline Gluca  Italy
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I have two separate PSUs and they are stacked to avoid the large biasing resistor for the 304TL (just think to the Loftin White and variants). The EXO99 choke and that Rx are fixing the bias for the 304TL, to make it more clear

801A grid:-9V
801A cathode: 0V
801A anode=304TL grid: +280V
304TL cathode: +330V
304TL anode: +1200V

The OPT is returned to the 304TL cathode.

I loved that amp but I am not using any more 304TL as they were way too hot

In the same amp I used GM70, 813, 304TL and 75TL. Going to give 845 a try soon.

Disclaimer: the high voltages can kill! Beware!

Gianluca
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Old 26th March 2009, 12:26 PM   #6
nhuwar is offline nhuwar  United States
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Thanks guy this is going to be a big help.



Nick
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Old 27th March 2009, 10:44 AM   #7
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Quote:
Originally posted by Gluca


Good luck with the OPT, not easy to find a good one.

Gianluca
That is a bit of an understatement. Either massive idle current, or massive B+ needed to reach anode-glowing dissipation. Insulation for multi-kV B+ is not good for leakage inductance, and neither is the size of the required cores for the SE power this one id capable of.

Neat thing to consider is only lighting half of the anodes and making a 152TL from it to start with. Slightly increased Miller from the unheated grids...and do use something bigger than a 6SN7 to drive it.
cheers,
Douglas
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Old 27th March 2009, 03:03 PM   #8
Gluca is offline Gluca  Italy
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Quote:
Originally posted by Bandersnatch

Neat thing to consider is only lighting half of the anodes and making a 152TL from it to start with. Slightly increased Miller from the unheated grids...and do use something bigger than a 6SN7 to drive it.
cheers,
Douglas
That would double also Rp making OPT's duties harder.

Gianluca
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Old 27th March 2009, 03:29 PM   #9
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That AlumRock amp looks attractive in a kinda commercial Bell & Howell way. The performance in output power is terrible however and this has to be due to insufficient drive and B+. This amp shud be making an easy 100 watts RMS/ch. I also do not like the total lack of attention in the way the IR from the output tubes will bake the black OPT's and other nearby surrounding components. Heat is the enemy to electronic components and many materials. A simple mirror finish SS heat shield would do wonders here.

I think the most practical answer to the high voltage on the OPT issue with these electric chair SET amplifiers is to parafeed the output stage and get the HV completely off the xfmer with a quality capacitor.
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Old 27th March 2009, 04:40 PM   #10
Gluca is offline Gluca  Italy
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Quote:
Originally posted by rcavictim
I think the most practical answer to the high voltage on the OPT issue with these electric chair SET amplifiers is to parafeed the output stage and get the HV completely off the xfmer with a quality capacitor.
A parafeed transfomer can be materially smaller (than a series feed one) and exhibits a larger inductance: lower and upper end gets better.

I am with you about heat: I am not using 304TLs for this very reason. Power is dissipated to bias the tube, to light it and to have a decent DC supply.

Gianluca
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