Today was the anual Tree Street Yard Sale event - Page 2

rongon · 31st August 2010, 03:00 PM

IIRC, Those big Marshall 4x12" cabs use four 16 ohm speakers in series-parallel so that they wind up at 16 ohms for each cab. Then when you make a "Marshall stack" out of two cabs and a "head" you're wiring the two cabs in parallel for 8 ohms total load.

--

TheGimp · 1st September 2010, 04:25 AM

I re-capped it, added a fuse and IEC connector with proper ground, and added a socket for the additional 12AX7 that is needed for the second channel.

I'm going to add terminals for the speakers, input connectors and a dual volume control next, then wire it up and get it going before making any other circuit changes.

I don't like all four output tube cathodes sharing one resistor but I'll leave that for now.

TheGimp · 3rd September 2010, 02:47 AM

Cleaned up, painted and added terminals.

I still need to add a pot on the input and wire up the gain stage and concertina for one channel, replace the ceramic coupling caps, and add the input RCA connectors.

Then I can find out if it will play.

wrenchone · 3rd September 2010, 04:29 AM

I'd clean up and paint that ugly power transformer. Cast iron gray engine enamel would look real nice next to the blue...

TheGimp · 3rd September 2010, 04:33 AM

Yea, it is not very photogenic is it?

I guess I'll have to pull it out, wire wheel it and shoot it with some paint. Fire engine red?

Day Glow Orange?

School Bus Yellow?

TheGimp · 3rd September 2010, 04:35 AM

On a brighter side, I found my stash of TRW 0.01uF 400V film caps so I can replace all the 0.01uF ceramic disk coupling caps.

wrenchone · 3rd September 2010, 04:41 AM

The blue is bright enough - I stand by my suggestion of cast iron gray, but then I usually try to go for quiet class instead of shock value.

Ian444 · 3rd September 2010, 04:56 AM

Nice work Steve. Should be nice for you to hear a PP amp for a change! I don't know about the 12AX7 for this duty (from my own expereince), it will work, but I find the 6N1P hard to beat, a tube you are more than familiar with. I guess you just want to hear how it originally sounded, plus with the cathode feedback, should be interesting. Bargains like what you picked up, seem to go for either free or 100 to 200 bucks from what I can see, over here.

Ian444 · 3rd September 2010, 04:59 AM

Definitely dayglo orange, and do the OT frames while you're at it.

TheGimp · 3rd September 2010, 05:15 AM

Canary yellow laminates and Day-glow orange end caps it is.

Yea, I 'm just curious to hear what it sounds like with the original cathode bias to all four tubes in one 135 ohm resistor. Got to be bad news.

I've got replacement 270 ohm 1W resistors with 330uF low ESR caps ready to replace the original 135 ohm resistor.

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31st August 2010, 03:00 PM	#11
rongon diyAudio Member Join Date: Jul 2009 Location: Down by the river	IIRC, Those big Marshall 4x12" cabs use four 16 ohm speakers in series-parallel so that they wind up at 16 ohms for each cab. Then when you make a "Marshall stack" out of two cabs and a "head" you're wiring the two cabs in parallel for 8 ohms total load. --

3rd September 2010, 04:29 AM	#14
wrenchone diyAudio Member Join Date: Feb 2004 Location: Silicon Valley	I'd clean up and paint that ugly power transformer. Cast iron gray engine enamel would look real nice next to the blue...

3rd September 2010, 04:33 AM	#15
TheGimp diyAudio Member Join Date: Aug 2009 Location: Johnson City, TN	Yea, it is not very photogenic is it? I guess I'll have to pull it out, wire wheel it and shoot it with some paint. Fire engine red? Day Glow Orange? School Bus Yellow?

3rd September 2010, 04:35 AM	#16
TheGimp diyAudio Member Join Date: Aug 2009 Location: Johnson City, TN	On a brighter side, I found my stash of TRW 0.01uF 400V film caps so I can replace all the 0.01uF ceramic disk coupling caps.

3rd September 2010, 04:41 AM	#17
wrenchone diyAudio Member Join Date: Feb 2004 Location: Silicon Valley	The blue is bright enough - I stand by my suggestion of cast iron gray, but then I usually try to go for quiet class instead of shock value.

3rd September 2010, 04:56 AM	#18
Ian444 diyAudio Member Join Date: Nov 2008 Location: Brisbane QLD	Nice work Steve. Should be nice for you to hear a PP amp for a change! I don't know about the 12AX7 for this duty (from my own expereince), it will work, but I find the 6N1P hard to beat, a tube you are more than familiar with. I guess you just want to hear how it originally sounded, plus with the cathode feedback, should be interesting. Bargains like what you picked up, seem to go for either free or 100 to 200 bucks from what I can see, over here.

3rd September 2010, 04:59 AM	#19
Ian444 diyAudio Member Join Date: Nov 2008 Location: Brisbane QLD	Definitely dayglo orange, and do the OT frames while you're at it.

3rd September 2010, 05:15 AM	#20
TheGimp diyAudio Member Join Date: Aug 2009 Location: Johnson City, TN	Canary yellow laminates and Day-glow orange end caps it is. Yea, I 'm just curious to hear what it sounds like with the original cathode bias to all four tubes in one 135 ohm resistor. Got to be bad news. I've got replacement 270 ohm 1W resistors with 330uF low ESR caps ready to replace the original 135 ohm resistor.

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