almost just another newbie thread...

dalcorn · 8th February 2006, 06:58 AM

but not quite... I'm a junior EE and am in my seconds electronics course, where we are doing opamps/feedback/etc. i've studied BJTs and FETs to some extent and read some material off of the newbie thread about how tubes work. i'm fairly comfortable reading schematics and what not.

that being said, i'd originally considered using the text online to design my own tube amp from parts i could find elsewhere; i'd also like to avoid a kit.

can anyone recommend a schematic or at least a tube I should look at using for a beginner tube amp? i'm comfortable working with high voltages if someone can point me to where i could find a suitable transformer for the design (i'm in the US).

i'd prefer to do as much as i could on my own aka as cheap as possible or else i would consider a kit.

ray_moth · 8th February 2006, 08:16 AM

Transformers are needed to provide power for the amp and, usually, to match the speaker's low impedance to the output tube's high impednace. A useful source of transformers of both types can be Hammond, especially for the beginner.

You really need to tell us a bit about what sort of thing you have in mind, before we can be of much help, e.g. do you want to build a headphone amp, guitar amp, hi-fi amp, low, medium or high power? This will help to determine the sort of tubes and transformers you might need or, at least, narrow the field a bit.

SHiFTY · 8th February 2006, 09:28 AM

You need lotsa iron: A power transformer with a 6.3V, 5V and HT windings (several hundred volts); a smoothing inductor for the power supply, and a pair of output transformers. You might be able to buy cheaply an old broken stereo amp or amp chassis to get these- or talk to a ham radio guy, they usually have boxes of them!

There are two basic types of amps: single ended and push-pull. Single ended are cheaper and simpler, but less power than push-pull. The output transformers are different for each type.

I would recommend building something like a push-pull EL34 or KT66 / 6L6 amplifier, with a B+ of 400VDC, cathode bias on the output tubes and a long tailed pair driver stage. This should get you around 20-30 quality Watts.

ToE · 9th February 2006, 12:19 AM

One potential source for transformers may be on your campus. If you have a theater dept. and they have a prop dept., they often have old consoles as props for shows. Offer to "lighten" the prop for them by removing the heavy bits and leaving the exterior pristine.

I've gotten some good iron and tubes this way. Most of the other parts should be disposed of, wire, caps, resistors, everything.

Should you get a nice pair or quartet of output tubes with output transformers, build that kind of amp whether push pull or single ended. I'm sure you can find nice schematics online for whatever tube types you discover, you might even find the original circuit.

SY · 9th February 2006, 12:32 AM

Start easy- a push-pull EL84 amp can be put together for a couple hundred bucks and can give you a nice, solid 10-15 watts. An exemplary circuit is the Bevois Valley, worked out in gory detail in "Valve Amplifiers," a book you should certainly own.

Edcor seems to make some nice output transformers for surprisingly low bucks. Or work the used market and try to find an old Dynaco SCA-35 or Stereo 35. Discard the guts, keep the transformers and case.

dalcorn · 9th February 2006, 02:39 AM

Quote:

Start easy- a push-pull EL84 amp can be put together for a couple hundred bucks and can give you a nice, solid 10-15 watts. An exemplary circuit is the Bevois Valley, worked out in gory detail in "Valve Amplifiers," a book you should certainly own.

Quote:

I would recommend building something like a push-pull EL34 or KT66 / 6L6 amplifier, with a B+ of 400VDC, cathode bias on the output tubes and a long tailed pair driver stage. This should get you around 20-30 quality Watts.

i think i'd like to try a push-pull EL34 designed for high fidelity.... i have an NAD 7155 receiver i can use as a phono stage...

http://www.amazon.com/gp/product/075...Fencoding=UTF8 -- this book?

SY · 9th February 2006, 03:20 AM

That's the one. There's a review by me in there, too.

ToE · 9th February 2006, 03:42 AM

Sounds like you want to take a step up from Sy's el84 Dynaco recommendations to the Dynaco ST70. Nice chassis, Great output iron, especially the original A-40 outputs of the early examples, many upgrade circuits available online...

A google search will yield hours of reading. The downsize, of course, is cost, even used. Triode Electronics was selling replacement iron for it at a reasonable price, Hammond has equivalents... As the other posters have noted, iron is often the major cost.

For many of us who started "as cheap as possible" wanting "high fidelity" the el-34 st70 was the answer. Maybe it still is. My mildy modded st70 is playing right now as my computer amp.

rickl · 9th February 2006, 04:24 AM

I wonder if El Cheapo would fit your requirements?
http://www.decware.com/cgi-bin/yabb/...num=1126228937

rick

arnoldc · 9th February 2006, 05:34 AM

Why don't you join these guys - EL34 schematic confusion

A DIYAudio designed EL34 amp

8th February 2006, 06:58 AM	#1
dalcorn diyAudio Member Join Date: Jul 2005 Location: Clemson, SC	almost just another newbie thread... but not quite... I'm a junior EE and am in my seconds electronics course, where we are doing opamps/feedback/etc. i've studied BJTs and FETs to some extent and read some material off of the newbie thread about how tubes work. i'm fairly comfortable reading schematics and what not. that being said, i'd originally considered using the text online to design my own tube amp from parts i could find elsewhere; i'd also like to avoid a kit. can anyone recommend a schematic or at least a tube I should look at using for a beginner tube amp? i'm comfortable working with high voltages if someone can point me to where i could find a suitable transformer for the design (i'm in the US). i'd prefer to do as much as i could on my own aka as cheap as possible or else i would consider a kit.

9th February 2006, 12:19 AM	#4
ToE diyAudio Member Join Date: Feb 2006 Location: Long Beach, California	One potential source for transformers may be on your campus. If you have a theater dept. and they have a prop dept., they often have old consoles as props for shows. Offer to "lighten" the prop for them by removing the heavy bits and leaving the exterior pristine. I've gotten some good iron and tubes this way. Most of the other parts should be disposed of, wire, caps, resistors, everything. Should you get a nice pair or quartet of output tubes with output transformers, build that kind of amp whether push pull or single ended. I'm sure you can find nice schematics online for whatever tube types you discover, you might even find the original circuit. __________________ Hugh

9th February 2006, 12:32 AM	#5
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	Start easy- a push-pull EL84 amp can be put together for a couple hundred bucks and can give you a nice, solid 10-15 watts. An exemplary circuit is the Bevois Valley, worked out in gory detail in "Valve Amplifiers," a book you should certainly own. Edcor seems to make some nice output transformers for surprisingly low bucks. Or work the used market and try to find an old Dynaco SCA-35 or Stereo 35. Discard the guts, keep the transformers and case. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

9th February 2006, 03:20 AM	#7
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	That's the one. There's a review by me in there, too. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

9th February 2006, 03:42 AM	#8
ToE diyAudio Member Join Date: Feb 2006 Location: Long Beach, California	Sounds like you want to take a step up from Sy's el84 Dynaco recommendations to the Dynaco ST70. Nice chassis, Great output iron, especially the original A-40 outputs of the early examples, many upgrade circuits available online... A google search will yield hours of reading. The downsize, of course, is cost, even used. Triode Electronics was selling replacement iron for it at a reasonable price, Hammond has equivalents... As the other posters have noted, iron is often the major cost. For many of us who started "as cheap as possible" wanting "high fidelity" the el-34 st70 was the answer. Maybe it still is. My mildy modded st70 is playing right now as my computer amp. __________________ Hugh

8th February 2006, 08:16 AM	#2
ray_moth diyAudio Moderator Emeritus Join Date: Jan 2004 Location: Jakarta	Transformers are needed to provide power for the amp and, usually, to match the speaker's low impedance to the output tube's high impednace. A useful source of transformers of both types can be Hammond, especially for the beginner. You really need to tell us a bit about what sort of thing you have in mind, before we can be of much help, e.g. do you want to build a headphone amp, guitar amp, hi-fi amp, low, medium or high power? This will help to determine the sort of tubes and transformers you might need or, at least, narrow the field a bit.

8th February 2006, 09:28 AM	#3
SHiFTY diyAudio Member Join Date: Jul 2002 Location: New Zealand	You need lotsa iron: A power transformer with a 6.3V, 5V and HT windings (several hundred volts); a smoothing inductor for the power supply, and a pair of output transformers. You might be able to buy cheaply an old broken stereo amp or amp chassis to get these- or talk to a ham radio guy, they usually have boxes of them! There are two basic types of amps: single ended and push-pull. Single ended are cheaper and simpler, but less power than push-pull. The output transformers are different for each type. I would recommend building something like a push-pull EL34 or KT66 / 6L6 amplifier, with a B+ of 400VDC, cathode bias on the output tubes and a long tailed pair driver stage. This should get you around 20-30 quality Watts.

9th February 2006, 04:24 AM	#9
rickl diyAudio Member Join Date: Jun 2004 Location: Minneapolis	El Cheapo? I wonder if El Cheapo would fit your requirements? http://www.decware.com/cgi-bin/yabb/...num=1126228937 rick

9th February 2006, 05:34 AM	#10
arnoldc diyAudio Member Join Date: Apr 2003 Location: Makati	Why don't you join these guys - EL34 schematic confusion A DIYAudio designed EL34 amp

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