• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

8 watt, 11MSB8 tube amp

Hello,

Just assembled my first diy amp kit from here http://www.s5electronics.com/tube2.html and need help troubleshooting. It did not smoke, blow up when plugged in. Tubes light up and I can faintly hear music coming out of the tubes! No hum or sound from speakers.

What to do next? Start at output transformers and check voltages? Go backwards from there? Start at input signals?

I did check each resistor before installing. All connections look good but what do I know. Would rather not send back to supplier until I am certain that some component is bad.

Your tips are appreciated!

Rick
 
Push-pull

Thank you for your response.

I believe the design is supposed to be push pull.

I have two output transformers both wired exactly alike at the moment.

Should I de-solder and switch the wiring around on both or leave one wired as is? Seems that I have wired them both incorrectly?

I assume any switching of wires to the output transformers is done safely since, assuming the wiring is incorrect now, nothing has burned up.

Your thoughts?

Thanks again from an aspiring diyer!

Rick
 
more questions

How can you tell what the correct wiring is? I do have a schematic and instructions but shouldn't I be able to check the pinouts from the tubes as well as the leads to the transformers to determine the proper wiring config for push-pull?

Perhaps you have a website reference that I can go to?

Thanks for reading!

Rick
 
Re: Push-pull

Hi Rick,

I believe the design is supposed to be push pull.
Maybe if you post the original schematic we can all take a look.
Should I de-solder and switch the wiring around on both or leave one wired as is? Seems that I have wired them both incorrectly?
Just try one. It'll only take 2 minutes and if it doesn't help, it won't hurt.
How can you tell what the correct wiring is? I do have a schematic and instructions but shouldn't I be able to check the pinouts from the tubes as well as the leads to the transformers to determine the proper wiring config for push-pull?
Since a picture says more than a thousand words, and I don't feel like typing a thousand words:
[IMGDEAD]http://www.ultranalog.com/temp/opt.gif[/IMGDEAD]

The dots in the schematic represent the winding direction. Change one of the primary windings (from the B+ supply to one of the pentodes) so that the phase of the induced signal into the core changes w.r.t. the other phase. If the circuit was in the 'bad' state, it'll now be good. If it doesn't help, change it back to the original state.
 
changing transformer leads

Hey thanks for the advice, Ultranalog!

I appreciate you hanging with me.

So, if I understand you correctly, I will switch the B+ (middle) lead on the primary with one (either) of the other leads on the same transformer. I will do this on only one of the output transformers--I have two (one for each channel).

I will scan the schematic and post tomorrow at work. Also, I will try to get digital photo of the amp for your review.

Thanks again,
Rick
 
changing transformer leads

Just changed the B+ with one of the output transformer leads and got no sound other than what is coming from the tubes.

(I did not switch both output transformers leads--just one pair of leads on one transformer.)

Nothing smoked. Output transformers do not heat up if that gives a clue. Tubes and power transformer do get hot, of course.

By the way, the schematic that you provided looks almost identical in config--I will attempt to post my schematic.

Any further ideas? Thanks for your attention.

Aspiring diyer,
rick
 
update on troubleshoot--11ms8 tube

Just a quick update

Signal traced the amp throughout and found the speaker posts (all) had been isolated from PCB pad by mistake with synthetic washers.

The amp sounds good and with my 106 db Altecs 605As is plenty loud! Can be too loud with this 8 watt amp. I will say, however, there is a slight hum to this amp.

Will still attempt to post schematic for those interested.

Aspiring diyer,
Rick
 
Re: update on troubleshoot--11ms8 tube

Signal traced the amp throughout and found the speaker posts (all) had been isolated from PCB pad by mistake with synthetic washers.
OK! So it was without load - just in a different way than I suspected. Good for you!
I will say, however, there is a slight hum to this amp.
My first tube amp was something like yours (4*6BM8) and also hummed. Raising the values of the caps, notably those feeding the input stage, helped considerably.
Guess we met in Aarhus Triode Audition Festival 2000, can that be?
I was there, yes. I've decimated my online life during the last year so I've forgotten many names and faces. Yours does ring a bell though.
 
ultranalog,
your 1st name starts with R, right?
I attended Aarhus together with Allen Wright and i was one of the two turntable nuts there. I had a beautiful mahogany diyTT with me. Was mostly running at Bert Doppenbergs Oris setup (except at the afternoon when the Ortofon guy demoed his Ortofon Jubilee).

Triode Audition Festival will take place around in Munich coming year, do you intend to come? I will be there.
 
your 1st name starts with R, right?
Hmm, now that you say it, I see I removed the name from my sig. Quite inconsiderate. Yes, it's Remco... my apologies.
I attended Aarhus together with Allen Wright and i was one of the two turntable nuts there. I had a beautiful mahogany diyTT with me. Was mostly running at Bert Doppenbergs Oris setup (except at the afternoon when the Ortofon guy demoed his Ortofon Jubilee).
Ah....!
[IMGDEAD]http://home.worldonline.dk/kbsp2/triodefestival2000/031l.jpg[/IMGDEAD]
Triode Audition Festival will take place around in Munich coming year, do you intend to come? I will be there.
No, I don't think so. First year I really enjoyed. Second year was disappointing, this year I did not attend and I heard it was even worse... maybe was never meant to be a repetitive event.

For you though, it'll be right around the corner - thus saving a lot of hauling trouble. Enjoy ;)
 
Altec 605A

Big box, closed, at the moment. (9+ cuft); variable Xover comes with the 605As, as you know. So, I change it with my mood and impulse.

These speakers are large and heavy but very efficient, me thinks. I hope to experiment with different sizes, vents, materials, damping configs, etc.

I don't know if it is the tubes and Altecs combo or simply the excitement of assembly but I was very pleased with the result!

Thanks for the attention.

Aspiring diyer,
rick
 
I found the schematic for the kit amp that I recently built. I must correct the mistake made for the tube number, however. It is 11MS8. I can't find any info on this tube, but it sounds really good (better than my Calrad sa-30b, Heathkit AA 40 and other 3 SS receivers. I was also mistaken on the hum--no hum from amp.

This was a really easy first diy project--my first and it worked! I can't really explain the electronics of it yet--so much to learn!

At $139 and a few hours time--what a blast! And you get a good amp to listen to.

Here's schematic. Hope you like it.

http://store.yahoo.com/lib/webtronics/km12sch.jpg

Rick
 
Remco
No, I don't think so. First year I really enjoyed. Second year was disappointing, this year I did not attend and I heard it was even worse... maybe was never meant to be a repetitive event.
i am quite sure that on a new location and with other guys organizing the show, it will become a new event.
And ... some of the Munich folks will have some superspecial amps .. i might have such too and some super special tonearms. And it could be quite interesting for you to compare your digital rig with Manfred Huber's or Thomas Mayer's one.
Hmmh, who knows, maybe you change your mind :angel: