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Old 31st December 2009, 05:10 AM   #1
trigger is offline trigger  United States
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Default el84 amp advice

hello my first post here, planing to build my first point to point tube amp from scrap parts. i gathered some old tube projects for years back to get some parts to harvest, a el84 12au7 amp i pulled from a old record player if i recall correctly, also available i have a tube radio with 2x 505c, 12ax7, and 7 9pin radio tubes.
the el84 amp was given some terminals, input jacks, and a power switch, nothing else was done, all original parts, i don't recall the make or model,(if any one knows please tell me).
i would like to find a project to make using these parts, just a simple amp with a separate simple pre. now the el84 sounds ok now, i just dont like all the control pots. perhaps i could remove the controls? noob here, i know my way around a schematic and iron. perhaps someone could recommend a good beginers project with no to little budget and my parts available?



i have here the pics of the amp, the circled red is the parts i added, the yellow is what id like to remove, if at all possible
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File Type: jpg amp.jpg (713.4 KB, 321 views)
File Type: jpg GEDC3483.jpg (653.0 KB, 296 views)
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Old 31st December 2009, 05:42 AM   #2
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Looks like a good candidate for an RH84. Adding a choke would be a good idea, and you'd need a 12AT7 for the front end (you should be able to find a used one cheap). That will leave you with a spare tube socket to add another gain stage (pre-amp) if needed (my RH84 don't need).

dave

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Old 31st December 2009, 11:27 AM   #3
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Default SS rectification?

Quote:
Originally Posted by planet10 View Post
Looks like a good candidate for an RH84. Adding a choke would be a good idea, and you'd need a 12AT7 for the front end (you should be able to find a used one cheap). That will leave you with a spare tube socket to add another gain stage (pre-amp) if needed (my RH84 don't need).

dave
The second RH84 amp pictured appears to use SS rectification?
Details??

Thanks

Doug
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Old 31st December 2009, 08:00 PM   #4
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Both use Greatz bridges, half vacuum (EZ81), half-SS. The second set of amps are monobloks and a fairly dramatic variation on the RH84. The front-end is triode strapped EF86, and the 2nd OPT is used as a plate load for a parafeed output stage.

dave
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Old 1st January 2010, 02:19 AM   #5
trigger is offline trigger  United States
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thank you for the advice, the rh84 looks to be my first project.
i live in the boondocks, and headed to the nearest city today, passing the only place i would ever see a tube(thrift store), i decited to go in to have a look, and to my surprise there was one and only one tube radio there, i picked it up and to my surprise it uses 12at7 tubes!!! what the luck of a drawl seriously this thrift store rarely ever has tube equipment and when it dose its usually overpriced organs.
so i picked up a untested pair of 12at7 along with a snazzy eric fm radio, for 10$

thus i shall start the rh84,,my first question is about the choke, where could i find one? like to salvage, is there any electronic devices with i suitable one i could pull.

there is a junk yard near by, i went and pulled all the tubes and speakers but still lots of transformers, there are council radios, ic and tube, tube tvs, lots of old junk. i bet somewhere in the mess i bet is a good choke for my project, but (excuse my noviceness) what the heck am i searching for? its a transformer but how can i tell what one i need? gather all them up bring them home and testing them would be a nightmare unless i had some precious knowlege that would lead me to a 5k ot? anything?
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Old 1st January 2010, 04:03 AM   #6
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Most of us, i expect, buy our chokes on-line. If you can find one in your junk box, just make sure it is at least 100mA.

If you have to buy one you'll want something like a Hammond 158M 10H 100mA. They are about $20 (+ postage). You can build it with a power resistor to start, but the choke is a simple way to really improve the PS.

dave
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Old 1st January 2010, 04:33 AM   #7
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i need to do some studying up on audio transformers, any recommendations on some free online literature on transformers that would help me get a grasp on how they work in the tube amp circuitry?

thank you much for the advice
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Old 1st January 2010, 04:36 AM   #8
trigger is offline trigger  United States
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at least for now i am confused how i can test a transformer for resistance to determine witch i need.
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