Replies to This Discussion

Permalink Reply by Mark on June 28, 2010 at 4:13am

I'm wondering if I understand your post correctly. Are you referring to the tube circuit in that PDF?

If so I would say it probably wasn't a wise move for a first build. You really do need to have good construction skills and be experienced with electronics before you try any sort of tube-based circuit. And an ancient circuit from a 1954 magazine is an especially bad place to start. How did you manage to get hold of the tubes it calls for?

I don't mean to be unhelpful, but perhaps you should put that circuit to one side and try something simpler - maybe one of the LM386-based designs such as the Ruby, Little Gem or Smokey.

By all means come back to your tube circuit when you've got a bit more experience under your belt. In the meantime you could try searching the internet for bulletin boards or discussion groups that specialise in tube amps (such things do exist). That's probably the best place to find people who can advise on troubleshooting your circuit.

Permalink Reply by Zed Steady on June 28, 2010 at 5:55am

It's been said that if brains were dynamite, I would be able to blow my nose. Sure maybe not an easy first project, but I learned a ton putting her together. I think the problem I'm having is routing the signal through the tube twice. I think as long as I'm careful to always discharge those caps, a little more experimenting will have her screaming in no time. Also, I feel that building solid state is as boring as buying it. The tubes GLOW man!
P.S. the tubes were a bear to find, but I bought up the last lot I could get my mitts on. Praise the internet for that.
Thanks for your help, if not the kind words of encouragement.

Permalink Reply by Mark on June 28, 2010 at 11:01pm

I didn't mean to be negative or discouraging. If you're determined to press ahead with that valve circuit then I hope you succeed - sometimes stubborness is an admirable quality.

I have a few further thoughts. First, it's worth figuring out more about that "bzzzzz" sound. Is it mains hum (a steady buzz at a frequency around 50 or 60 Hz)?. Or is it clearly at a different frequency to mains hum or does the frequency vary, in which case you might be experiencing the effect I've heard described as "motorboating" - this is when amps turn into oscillators (which I think tends to be due to feedback problems within the circuit). Or is it just random noise with no clear single frequency?

Also, I read through the description of that circuit again and it uses the chassis as the ground (which has some very scary aspects to it!). If the chassis is part of the circuit that might have something to do with the noise (eg. by providing a route for shorts or for external noise to get in).

Also, does the amp work at all? What I mean is, if you plug a guitar in one end and a speaker in the other can you hear any amplified guitar sound along with the bzzzz, or is it just bzzzzz and nothing else?

PS. I disagree with you totally about solid state. There's definitely a lot of interesting stuff you can do with transistors (especially JFETs). Always be sceptical of so-called traditional wisdom such as the widespread belief that tube amps are the only true way to get a good sound. Sure there are some great sounds that come from tubes, but there are other great sounds which originate from solid state circuits.






Zed Steady said:

It's been said that if brains were dynamite, I would be able to blow my nose. Sure maybe not an easy first project, but I learned a ton putting her together. I think the problem I'm having is routing the signal through the tube twice. I think as long as I'm careful to always discharge those caps, a little more experimenting will have her screaming in no time. Also, I feel that building solid state is as boring as buying it. The tubes GLOW man!
P.S. the tubes were a bear to find, but I bought up the last lot I could get my mitts on. Praise the internet for that. Thanks for your help, if not the kind words of encouragement.

Permalink Reply by Zed Steady on June 29, 2010 at 5:13am

You are entirely correct about solid state. I think the kitsch factor of hand building a 1 watt tube amp that would fit in a cigar box was too much for me. I had to try it.
I built the circuit twice. Once with the chassis as ground, and again with a common plate to the negative that I insulated for safety.
The buzz is similar to main buzz but it appears to max out the speaker. It literally shook its self off the table the first time I turned it on. And it makes the buzz noise regardless if there is an input connected of not. It is a constant noise, sort of like that terrible vuvulela drone. I get squips and cracks if I jostle the volume knob around, so perhaps I could try a pot with a different Ohm setting. Also, I used 3 separate capacitors instead of the triple section.
Thanks for talking with me about this, byt he way. I'm glad someone has an interest. Hey, maybe if I can get it all figured out, I'll send one your way. Thanks again.

Permalink Reply by Mark on June 29, 2010 at 9:43am

Seems like you can probably rule out a simple mains hum problem. I guess it's some sort of feedback or short or instability. Sadly I can't be of much help on that.

Have you got a spare tube(s) and if so have you tried swapping them with the one in your circuit. I did a quick google on "117L7" (ie. the type of tube specified in the article) and I came up with a few discussions about people using them in old radio circuits. Several posts were about faults in parts of the tube.

Might be worth seeing if you can find someone who can test tubes for you.



Zed Steady said:

You are entirely correct about solid state. I think the kitsch factor of hand building a 1 watt tube amp that would fit in a cigar box was too much for me. I had to try it.
I built the circuit twice. Once with the chassis as ground, and again with a common plate to the negative that I insulated for safety.
The buzz is similar to main buzz but it appears to max out the speaker. It literally shook its self off the table the first time I turned it on. And it makes the buzz noise regardless if there is an input connected of not. It is a constant noise, sort of like that terrible vuvulela drone. I get squips and cracks if I jostle the volume knob around, so perhaps I could try a pot with a different Ohm setting. Also, I used 3 separate capacitors instead of the triple section.
Thanks for talking with me about this, byt he way. I'm glad someone has an interest. Hey, maybe if I can get it all figured out, I'll send one your way. Thanks again.

Permalink Reply by Mark on July 7, 2010 at 11:42am

http://www.runoffgroove.com

http://www.beavisaudio.com

Gage said:

where can i find plans for LM386-based designs such as the Ruby, Little Gem or Smokey?

Permalink Reply by Greg on July 8, 2010 at 7:14am

I just found this group and think I might just like it. First of all here's a place for those 117L7 tubes....TubeDepot.com nos tube @ $7.95 each. I buy alot of supplies ( I repair,hot rod and sometimes destroy amps as a hobby) from TubeDepot. They are quick shipping and have good prices. They also sell resistors,capacitors,bare boards for DYI builders and a bunch of other stuff some of you might find yourself needing. BTW I'm in the process of designing an 8watt or so tube amp. Getting everything into a cigarbox might be a challenge but my prototype is sounding pretty good and with a little tweaking with some cap values and such it might just be a hit.

Permalink Reply by Nelson Filho on July 19, 2010 at 8:31pm

Hey man you are using the correct transformer (radio) with 2500 ohms input and of 4 ohms output? The speaker is 4 ohms impedance?
This may be causing the problem ... Today I bought on ebay a lot of tubes, which are not identical, but I hope to make it work, I live in Brazil then it will take time. The project looks good and interesting for being a micro amp tube.

(Sorry my poor english)

Zed Steady said:

You are entirely correct about solid state. I think the kitsch factor of hand building a 1 watt tube amp that would fit in a cigar box was too much for me. I had to try it.
I built the circuit twice. Once with the chassis as ground, and again with a common plate to the negative that I insulated for safety.
The buzz is similar to main buzz but it appears to max out the speaker. It literally shook its self off the table the first time I turned it on. And it makes the buzz noise regardless if there is an input connected of not. It is a constant noise, sort of like that terrible vuvulela drone. I get squips and cracks if I jostle the volume knob around, so perhaps I could try a pot with a different Ohm setting. Also, I used 3 separate capacitors instead of the triple section.
Thanks for talking with me about this, byt he way. I'm glad someone has an interest. Hey, maybe if I can get it all figured out, I'll send one your way. Thanks again.