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Brainstorming something fun to do with a type 27

thorpej

thorpej

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I have a couple of old radios that use type 27s (or, in the case of my Sparton, can be adapted to use 27s with a power supply tweak, because the original 484/485 is now unobtanium), and I recently picked up a small lot of a dozen or so 27s to have a few spares. Turns out that all of the tubes in the lot are in really good working condition, so now I'm thinking that, in addition to having a few spares for the old radios, I could do something fun with a few of them, as well.

These tubes only have a mu of 9, so I'm not expecting to move mountains with them or anything...

So, toss your ideas this way, folks...
 
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Dennis Had makes a nice preamp based on the 27 tube. I just heard one yesterday hooked up to a Inspire SET amp. Quite nice.

BillWojo
 
They can make a very nice preamp, as long as you can find quiet 27's. ST aren't too bad, but a lot of the globes are noisy,
 
BillWojo said:
Dennis Had makes a nice preamp based on the 27 tube. I just heard one yesterday hooked up to a Inspire SET amp. Quite nice.

BillWojo
Click to expand...

I'm waiting for a chassis to come back from Dennis Had's chassis tech to build a 27/56 based preamp from a design that I came up with and Dennis has "approved". I don't have a copy of the schematic on this laptop, but I'll see if I can remember to post it later....
 
Found it....



Pretty simple design actually. 56's are a direct drop in for the 27. Uses an OD3 voltage regulator in the power supply, where Dennis likes to use Zeners. 1st cap off the 80 rectifier is now a 16uF motor run/oil filled. IIRC, ripple voltage is down around 1-2 uV...may also change it to dual output as well.
 
analog addict said:
Found it....



Pretty simple design actually. 56's are a direct drop in for the 27. Uses an OD3 voltage regulator in the power supply, where Dennis likes to use Zeners. 1st cap off the 80 rectifier is now a 16uF motor run/oil filled. IIRC, ripple voltage is down around 1-2 uV...may also change it to dual output as well.
Click to expand...

Cool. I think I'd probably add a cathode follower for the outputs, but I dig it.

Hm, has anyone done a series-filament arrangement with these tubes before? 5V transformers are easier to find than 2.5V.
 
thorpej said:
Hm, has anyone done a series-filament arrangement with these tubes before? 5V transformers are easier to find than 2.5V.
Click to expand...

I would advise against it myself because the main source of "Hum/Noise" with these is related to the filaments.

Maybe someone else can chime if they have tried it. Just from my point of view its hard enough to get these quiet with 2.5 volts alone.

Frannie
 
An UTC A-24 or H-113 after the cap would be the best if you need a low impeadance , i have a bushel basket full of 27s best used in vintage radios . Usually like to stay with octals if making something from scratch but will make an exception for the odd 300B .
The microphonics from early tubes is a big turnoff for me .
 
battradio said:
An UTC A-24 or H-113 after the cap would be the best if you need a low impeadance , i have a bushel basket full of 27s best used in vintage radios . Usually like to stay with octals if making something from scratch but will make an exception for the odd 300B .
The microphonics from early tubes is a big turnoff for me .
Click to expand...
The 6P5 would be a good Octal choice "IMHO" if you are into Type 27 line stages and want some Octal that is cheap enough.

Hope the OP does not mind this.

Frannie
 
I'm curious to see how it goes. I've listened to quite a number of Dennis' 27 based preamps and haven't noticed any wonky 27s in any of them... And yeah my build has two 2.5V transformers shown in the PS....
 
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