Little Red--new build

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Jana
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Joined: Sun Sep 07, 2008 10:40 pm
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Little Red--new build

Post by Jana »

A new build.

This is a single ended (6550) with two 12AX7's. The chassis is from RJ, the power and output transformers are from David Allen, and the choke (the red one) is from my stash.

The enclosure is from Taylor at Amplified Nation (he does wonderful work!).

The speaker is a Eminence Legend 1258. I am not pleased with that speaker and have ordered a Cannabis Rex.

:)
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John_P_WI
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Re: Little Red--new build

Post by John_P_WI »

Looks great Jana. Good to see you back.
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M Fowler
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Re: Little Red--new build

Post by M Fowler »

Nice amp Jana and good to see you building. :)
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martin manning
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Re: Little Red--new build

Post by martin manning »

Hi Jana, that red thing is the choke? It's huge!
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cbass
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Re: Little Red--new build

Post by cbass »

Looks slick.
Jana
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Re: Little Red--new build

Post by Jana »

Thanks Everybody.

Martin,
Yes, the choke is big--lol--it is rated 200ma and 10H. I think the DCR is around 100 ohms--I forgot, haven't measured it lately. I have it prior to any of the B+ nodes (including the OT). No hum in this amp. :)

I have been carrying this choke around for 30 years waiting for a perfect build for it.
Jana
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Location: Minnesota

Re: Little Red--new build

Post by Jana »

I forgot to mention--11 watts clean and 21 watts pushed to the max.
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cbass
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Re: Little Red--new build

Post by cbass »

What your plate voltage?. I've been interested in doing a big bottle SE amp
Jana
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Location: Minnesota

Re: Little Red--new build

Post by Jana »

cbass,

I used the TP24 power transformer from Allen Amps.

The voltage after the diodes (47uf filtering) is 387.

The voltage after the choke (another 47uf) is 370. This is the node that feeds the OT (TO 15 from Allen Amps).

Then I have a 2k7 -- 5 watt for the screen node of the B+. 335 volts at this node. I have a 1K feeding the screen of the 6550 from this node.

The cathode resistor is 250 ohms. 27 volts bias.

I forgot to measure the actual plate voltage (well, I did when I was testing, but forgot to write it down).
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cbass
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Re: Little Red--new build

Post by cbass »

Thanks Jana
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Structo
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Re: Little Red--new build

Post by Structo »

Very pro looking build Jana.

Good to see you back on TAG.
Tom

Don't let that smoke out!
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cbass
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Re: Little Red--new build

Post by cbass »

Structo wrote:Very pro looking build Jana.

Good to see you back on TAG.
Yea we could use a little class around here :P
Bob S
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Re: Little Red--new build

Post by Bob S »

Great looking build Jana.
Welcome back - we missed you.
Now where's Lefty ?
Why Aye Man
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David Root
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Re: Little Red--new build

Post by David Root »

Jana, glad to see you are back. +1 on the 10H choke, SE operation needs that 10H goodness, and on the power tube plate all right.

I recently finished an SE KT66, different pre-s (5879) and I used a 10H 100mA choke (Triad C7X) and mine is dead quiet too.

Just curious, how did you select your choke for this build? Did you run a PSUD2 simulation first to see what the RMS ripple would be, or just grabbed it, knowing that SE needs more Henries than PP?
I ran the sim and it was pretty clear from that that 10H is the magic number.

I now have a 10H 200mA for a 2xKT88 SE, it's as big as the one in your pic.
Jana
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Re: Little Red--new build

Post by Jana »

cbass, Yes, we could use some class around here--unfortunately, I'm not the one to bring it!

David, How did I select the choke? It went something like this: 30 years ago I was browsing through parts at an electronics store in Los Angeles. I saw this big choke and thought, Wow, that's really big, and only two wires! I want that.

This is a Triad choke as well. I forget the part number. It had gray end bells but I painted them red. Where did you find a 10H / 200ma. choke?
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