Is this do-able?

deafdumbblind · 9th July 2011, 09:14 AM

I found these two units in the trash locally here in Japan this week. And old National mono amp and matching mono radio.
I'd love to frankenstein them together to make a stereo. (Two mono blocks under one hood)
Will I need a control board like the one in my Dynaco st-70?
Any help is much appreciated!

alexg · 9th July 2011, 03:06 PM

Both seems to be EL34 PP?

If they are and the power transformer and OPT are identical, then it is to doable to make two monoblocks.

deafdumbblind · 10th July 2011, 06:10 AM

In the second photo is the PCB the pre amp?

Wavebourn · 10th July 2011, 06:32 AM

Quote:

Originally Posted by deafdumbblind

In the second photo is the PCB the pre amp?

Phase splitter. It is part of power amp. Receiver contains the same, plus some extra parts needed for radio. You probably can find schematics in BAMA archive.

deafdumbblind · 11th July 2011, 12:22 AM

Can anyone point me in the right direction on what I need?

6L6 · 11th July 2011, 03:46 AM

The good thing is that the output section of both those units seem to be identical. It will make the conversion into 2 monoblocks fairly painless. Choose your favorite schematic and go for it!

deafdumbblind · 11th July 2011, 06:22 AM

What would you do? I don't have enough knowledge on these matters to make an educated decision!

indianajo · 06:25 PM

read the high voltage for newbies section of the sticky thread at the top of this forum. Buy a ST70 "improvement" driver PCB like the KTA here Classic Valve Design - Dynaco Clone and Original Design Boards and Repair Kits - Dynaco ST-70 Modifications .Uses readily available 12AX7 etc dual triodes. Hook the four outputs (plates) of this through .1 caps to the input grids of the four output tubes. hook up the feedback from output transformer back to the input PCB. See dynaco ST70 for sample drawing. Remove plate feeds to the old driver sockets, select (by getting it wrong) dropping resistor to feed B+ supply of new driver PCB to get about 290 V in to the driver plastes. Note new design 1/4 & 1/2 watt resistors are too short for 450 V, must buy 2 W resistors to get 450 volt rating. Hook up the 6VAC to filaments as normal, remove plate feeds to old driver and make sure no power transformer windings are unterminated.
Or draw out the old schematic (or download it) and do something more creative.
You'lll need at least a DVM with a 600V scale and probe. I like the non-autoranging ones.

deafdumbblind · 11th July 2011, 10:40 PM

Yes! I can do this! Thanks for taking the time to make a hit list! I read the high voltage for newbies section, thanks and I'll write about my progress.

11th July 2011, 03:46 AM	#6
6L6 diyAudio Member Join Date: Oct 2010 Location: Denver, Colorado	The good thing is that the output section of both those units seem to be identical. It will make the conversion into 2 monoblocks fairly painless. Choose your favorite schematic and go for it! __________________ Pass Labs Pearl Phono -- Pass B1 Preamp -- Pass F5 amplifier -- Pass Labs Pearl 2

11th July 2011, 06:21 PM	#8
indianajo diyAudio Member Join Date: Jan 2010 Location: Jeffersonville, Indiana USA	read the high voltage for newbies section of the sticky thread at the top of this forum. Buy a ST70 "improvement" driver PCB like the KTA here Classic Valve Design - Dynaco Clone and Original Design Boards and Repair Kits - Dynaco ST-70 Modifications .Uses readily available 12AX7 etc dual triodes. Hook the four outputs (plates) of this through .1 caps to the input grids of the four output tubes. hook up the feedback from output transformer back to the input PCB. See dynaco ST70 for sample drawing. Remove plate feeds to the old driver sockets, select (by getting it wrong) dropping resistor to feed B+ supply of new driver PCB to get about 290 V in to the driver plastes. Note new design 1/4 & 1/2 watt resistors are too short for 450 V, must buy 2 W resistors to get 450 volt rating. Hook up the 6VAC to filaments as normal, remove plate feeds to old driver and make sure no power transformer windings are unterminated. Or draw out the old schematic (or download it) and do something more creative. You'lll need at least a DVM with a 600V scale and probe. I like the non-autoranging ones. __________________ Dynakit ST70, ST120, PAS2,Hammond H182(2 ea),H112,A100,10-82TC,Peavey CS800S,SP2-XT's, T-300 HF Projs, Steinway console, Herald RA88a mixer, Wurlitzer 4500 Last edited by indianajo; 11th July 2011 at 06:25 PM.

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9th July 2011, 03:06 PM	#2
alexg diyAudio Member Join Date: Jan 2005 Location: Philippines	Both seems to be EL34 PP? If they are and the power transformer and OPT are identical, then it is to doable to make two monoblocks.

10th July 2011, 06:10 AM	#3
deafdumbblind diyAudio Member Join Date: Jan 2007	In the second photo is the PCB the pre amp?

11th July 2011, 12:22 AM	#5
deafdumbblind diyAudio Member Join Date: Jan 2007	Can anyone point me in the right direction on what I need?

11th July 2011, 06:22 AM	#7
deafdumbblind diyAudio Member Join Date: Jan 2007	What would you do? I don't have enough knowledge on these matters to make an educated decision!

11th July 2011, 10:40 PM	#9
deafdumbblind diyAudio Member Join Date: Jan 2007	Yes! I can do this! Thanks for taking the time to make a hit list! I read the high voltage for newbies section, thanks and I'll write about my progress.

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