Recent Posts

1

Guitars / Guitar tools

« Last post by rake on October 23, 2025, 09:13:46 pm »

Just got an email from Stew Mac and they're having a tool sale. 20% - 50% off.
One super deal is the Fret Kisser ar 50% off. (not a sponsor)
It's wort a look.

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Tube Amp Building - Tweaks - Repairs / Re: Hum and Buzz in Cordovox Build

« Last post by AlNewman on October 23, 2025, 08:11:29 pm »

I'm sure you've already tried the simplest option, which is to remove all the tubes, and install them from the power section back to isolate where the problem originates.

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Tube Amp Building - Tweaks - Repairs / Re: Kay Model 777 Reverberation

« Last post by dbishopbliss on October 23, 2025, 07:59:43 pm »

One other thing... if you plug the cable from the footswitch into you amp (yes, you read that correctly) it sounds like an overdrive/fuzz pedal. It's a cool effect but I'm not sure why it does that. Any thoughts?

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Tube Amp Building - Tweaks - Repairs / Kay Model 777 Reverberation

« Last post by dbishopbliss on October 23, 2025, 07:52:38 pm »

I got this cool little reverb off of CL today. I plugged it in and it sound REALLY good. Not quite like a Fender Reverb. More plate-like than the drippy surf spring reverb sound but I dig it.


I'm wondering if it is safe to use...

• I'm thinking that I should probably add a 3 prong power cord but maybe that's not necessary.
• There doesn't seem to be any sort of fuse... maybe that's bad.
• The power is turned on using a switched pot. Anything to be concerned about?

There doesn't seem to be any information about these boxes our there. The circuit is different from the Model 710 that in the schematics library. What are your thoughts?


Thanks!

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Tube Amp Building - Tweaks - Repairs / Re: Hum and Buzz in Cordovox Build

« Last post by scstill on October 23, 2025, 07:20:28 pm »

Yeah that circuit is not elevating the CT so something not working correctly, unless it is not why its there.
BTW the cap is 0.22uf wrong on the schematic.
But, there is no change in the hum when jumping xfmr CT to ground. So that is not the issue apparently.

There is another 7vct coil on the transformer (not used in this guitar conversion) that was used for the Cordovox Tone Generator Tubes and its CT was also connected thru 100k to the CT of the 6.3v winding (diagram attached). But when I reconnected that CT it changed nothing.

The biggest (really big) reduction in hum is when a ground wire is close to the preamp glass. Also eliminates the loud pot click at full on. Maybe a tube shield is in order. Or a redo of the preamp circuit. Most everything in this build is as it was in the Cordovox except new filter caps and revised signal path adding tone stack and MV in Preamp and some improved star grounding.

6

Tube Amp Building - Tweaks - Repairs / Re: 5E3 Bias

« Last post by passaloutre on October 23, 2025, 06:02:16 pm »

What is the cathode voltage? Assuming 250r bias resistor?

Is 56mA per tube, or both combined?

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Tube Amp Building - Tweaks - Repairs / 5E3 Bias

« Last post by dpm309 on October 23, 2025, 05:37:09 pm »

My 5E3 build (1st amp I built several years ago) was experiencing crackling on the volume pots. Took it apart and cleaned the pots and is working. While I had it on my bench, I checked the voltages and bias.  A few years ago I performed the Simplified Dumble 5E3 Tweedle Mods on it. The amp sounds great with this mod. I replaced the 5Y3 rectifier with a GZ34 along with other mods. My plate voltage on the power tubes is 372VDC which gives me a bias of 56ma. This seems high for a 6V6 but the amps sounds great and have not had any issues with the power tubes.  Is 56ma too high? Will this affect the life of the power tubes?

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Tube Amp Building - Tweaks - Repairs / Re: Hum and Buzz in Cordovox Build

« Last post by shooter on October 23, 2025, 05:34:34 pm »

not a theory guy so;


the "charged" cap n R form an artificial ground, above actual chassis ground.  easy enough to verify, set up your meter for VDC, measure the top of cap/R juntion to chassis ground.


me, I would lift that connection from CT n temp ground CT to chassis, just to eliminate it as a problem, when all the good things are verified, then only the bad thing is left.   

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Tube Amp Building - Tweaks - Repairs / Re: Hum and Buzz in Cordovox Build

« Last post by Wonder2121 on October 23, 2025, 04:16:32 pm »

I dont see how its elevating anything, it's not connected to a DC source...
Read this https://www.valvewizard.co.uk/heater.html

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Tube Amp Building - Tweaks - Repairs / Re: Adding gain stage

« Last post by tubeswell on October 23, 2025, 03:34:38 pm »

Here's how Ceriatone do it