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Tubelab Discussion and support of Tubelab products, prototypes and experiments

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Old 1st June 2009, 11:29 PM   #21
BillEpstein is offline BillEpstein  United States
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Just to muddy the waters, the Magnequest Robin Hood RH-80s look like a good choice for $99 per.

http://www.magnequest.com/products.htm
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Old 2nd June 2009, 12:15 AM   #22
rknize is offline rknize  United States
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Quote:
Originally posted by PaulyT
I really can't judge whether the power would be sufficient... I'm guessing not, hence my interest in the 300B. But you've got me at least considering the 45 as an alternative.
Really depends on the sensitivity of those horns. The TSE with 45s can fully drive my 98dB speakers to uncomfortable volume levels without difficulty. They work well for "critical" listening by myself, but are lacking when I want to rock and roll. I now have a working SSE for that.
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Old 2nd June 2009, 12:36 AM   #23
oldmanStrat is offline oldmanStrat  United States
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I'll be building my SE with the Rknize transformer (since we are naming transformers now) ... as soon as they finish winding it.

I'll also be using the 5k transendars that I have from the SSE before I got the big OPTs. And I also have the EH-300B's...

This amp will go in my office, so I won't need large amounts of power.
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Old 2nd June 2009, 02:04 AM   #24
Evenharmonics is offline Evenharmonics  United States
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Quote:
Originally posted by PaulyT

2) The power transformer, guess Hammond 276X is still a good choice? Never shopped for transformers before, so I have no idea what alternatives there are...


4) Will do the R4 choke mod - is the Triad C-14X still the way to go here?

5) For the supplementary cap at C5, docs say "I added a large 100 uF, 370 volt AC polypropylene motor RUN cap to my 300B amp." Anyone know where to find one of these? Not sure if digikey sells them, mouser seems to go up only to 80 uF in this class... (and wow, these aren't cheap!)
2) Go with Edcor or Electra-Print. I've tried a few Hammond power t and I personally cannot recommend it.
4) Yes, especially for high efficiency speakers.
5) ebay has good number of listing (at least when I looked).

Here's a tip I posted on dealing with input tube socket.
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Old 2nd June 2009, 07:45 PM   #25
PaulyT is offline PaulyT  United States
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Haven't heard back from Edcor. I'm working with Jack from Electra-Print on a quote for a set of three transformers, two output and one power. Here's what I'm looking at:

2 x OPT: 5k, 100ma to 6 ohms ($125 ea.)

1 x power: 660vct @ 150ma, 5v @ 3a, 6.3v @ 5a ($141)

Before I pull the trigger, does this seem reasonable for what I'm building? I know I don't necessarily need the full power for driving just HF horns, but I'd rather build a more general amp just in case (like if plans change or I want to sell it someday). And yes EP is a little more $$ but this is my first amp and I'd rather get something known to be solid and dependable, rather than experiment with cheaper (or more expensive and "esoteric") stuff right now.
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Old 2nd June 2009, 08:53 PM   #26
rknize is offline rknize  United States
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You'll need to call Edcor to get a timely response. They are very busy and she is very helpful when you get her on the phone.

That said, you probably can't go wrong with the EPs. I had the UBT-2's from a different project that didn't get off the ground. Had I not had them, I would have gone EP.
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Old 2nd June 2009, 11:06 PM   #27
PaulyT is offline PaulyT  United States
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Making progress, got the tubes ordered, and will probably order the EP transformers tomorrow.

Working through some of the other parts, I notice that C9,11 are .22uF caps in the schematic/specs, but the AES part # is actually a .47uF... and seems to be the same as what's pictured in at least one of the images in George's instructions. How do I decide what cap to use here? Should I just go with the .47 from AES?
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Old 2nd June 2009, 11:51 PM   #28
agent.5 is offline agent.5  United States
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Quote:
Originally posted by PaulyT

2 x OPT: 5k, 100ma to 6 ohms ($125 ea.)

You may want to wait for a response from tubelab before you order the transformers. I think you want the OT to be gapped to 60ma instead of 100ma.
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Old 3rd June 2009, 12:13 AM   #29
PaulyT is offline PaulyT  United States
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Quote:
Originally posted by agent.5



You may want to wait for a response from tubelab before you order the transformers. I think you want the OT to be gapped to 60ma instead of 100ma.

I'm confused, I thought the gapping affected the voltage, and the amp rating was simply the max current it could handle? For example, the UBT-2 is 5k primary, 4/8/16 secondary, with 110mA max current. That's pretty close to the OPT specs I posted.

?
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Old 3rd June 2009, 12:18 AM   #30
agent.5 is offline agent.5  United States
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Quote:
Originally posted by PaulyT



I'm confused, I thought the gapping affected the voltage, and the amp rating was simply the max current it could handle? For example, the UBT-2 is 5k primary, 4/8/16 secondary, with 110mA max current. That's pretty close to the OPT specs I posted.

?

gapping only affect the current and operating point of the output tube. If you 300B is operating at 60ma, you want the gap to be 60ma. You always want the gap to be as small as possible. In fact, when it comes to OT, size does matter. The smaller the better, for the core size and gap size.
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