Build Your Own Clone Message Board

I just finished my 18w TMB build the other night. Last night I went through double checking my wiring, looking for shorts, double checking component values etc.

I noticed my filament wiring was shorted to ground. So I disconnected the green wires from the Daisy chain, tested each with my DMM and I'm getting g continuity to ground from each of the green wires coming out of the transformer.

I disconnected all of the wires going to ground coming from the transformer, and I still was getting continuity to ground from the green filament wires.

This can't be right, right?

That is correct. The 6 volt (green) and 5 volt (yellow) ac circuits will show as an open circuit using continuity when the center taps are grounded. Best way to check your wiring is to disconnected the transformer wiring from the heater daisy chain, then check the daisy chain for shorts to ground without the transformer connected.

Best way to test that part of the transformer is to measure AC volts (not DC) across the two wires (like across a tube socket) with no tubes installed. You should have less than 7 volts or so there with no tubes installed.

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MasterDelayer/Reverbrador/Ampaholic/TopJacker

Hi Morgan

Thanks for the response. I have a basic understanding of electronics (2 course in college 10 years ago, but that's come and gone ha!), and have read quite a few journals on tube amps prior to the build. This one just puzzled me.

Before I left for work this morning, I did a few more tests. I disconnected the green wires from the filament circuit. Both wires (coming out of the transformer) are showing continuity to ground. I disconnected the green/yellow center tap. Still showing continuity to ground. Does that make sense?

No, it doesn't really make sense. I believe that the 6 volt circuit should be isolated from the transformer core when all 3 taps are disconnected. But I don't really know that (perhaps the heater center tap is tied to the HV center tap?) and I don't think anyone here really knows that for sure either. The problem is that transformers are inductors, and you can't really make many direct measurements on them with a DMM. We can mostly only make indirect measurements, which means we usually act off of symptoms.

In this case, it seems like you don't have actual symptoms (no power, one of the secondary circuits not working, excess heat, smoking, etc) and we're just sort of fretting about a resistance reading. Plus, if the transformer is already bad, we can't make it any worse by plugging it in.

So this is what you do: reconnect the heater circuit. Do not install any tubes. Make sure the transformer wiring is correct. Make sure you've got the correct fuse installed (2 amp slo blo). Plug the amp in and turn it on (put it on a current limiter if you've got one). When you turn it on, the indicator light should come on. This will immediately tell you if the heater circuit is working because the indicator works off the heater circuit. If there is an internal short in the transformer either the fuse will blow right away, or you will hear some gurgling in the transformer and maybe see some smoking (or the light bulb will glow brightly if you have a limiter).

If all seems well, turn the amp off, install a 12AX7 into V1, turn it back on and see if the 12AX7 heater begins to glow. If it does, install another 12AX7 into V2 and check again. If all seems well at that point, proceed with the rest of the BYOC instructions.

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MasterDelayer/Reverbrador/Ampaholic/TopJacker

So, the wiring of the power section seems to be working!

With the amp in stand by mode, all tubes did heat up. (Started with the ez81, then power tubes, and pre amp tubes 1 by 1)

I'm measuring 122 VAC in frmo the wall. 310VAC to Pin 1 and 307 to pin 7 in stand by mode. I am measuring 278VDC at pin 3. According to the instructions book, I should be measuring 340 here in standby mode. However, the chart below shows 283, which is more in line with what I am measuring.



Tomorrow I am going to triple and quadruple check my wiring, and fire it up! i am excited.

Well, after double and triple checking my wiring, component values, and fixing a few cold solders my build is complete!!

First thoughts: Wow this is loud! I have the amp in my basement and can't go past 2-3 on the volume.

I do have a few concerns:

1. the "Normal" channel seems a bit dull. Sounds like the TONE is rolled back even though it is on 10. I can definitely hear the tone rolling off even more as I lower the TONE knob, but it seems to lack clarity when at 10. Not sure if this is a "break in" issue that will go away with time, or if I have an error somewhere.

2. The master volume only controls the TMB channel, right?

I'm feeling fairly confident after this build. Now if I can only learn how to play guitar LOL!

1. No break in issue. Check you component placement; particularly the value of the caps connected to the tone and vol controls.

2. Correct. It's better to think of the TMB channel 'volume' control as a gain control, and the 'master volume" control as the volume control for the TMB channel.

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MasterDelayer/Reverbrador/Ampaholic/TopJacker