Recent Posts

61

Tube Amp Building - Tweaks - Repairs / Re: Univox 202R Amplifier making noise

« Last post by passaloutre on September 08, 2026, 07:02:26 am »

What a weird phase inverter. I may have to make this one.

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Tube Amp Building - Tweaks - Repairs / Re: Tweed BluesMeister needs a tweak

« Last post by AlNewman on September 07, 2026, 11:17:18 pm »

Do you have a schematic of a working amp that you started with?  Can you trace the signal back to see where you lose a clean sine wave?

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Tube Amp Building - Tweaks - Repairs / Re: Weber Princeton Reverb build - another problem after it’s been running great

« Last post by leevc5 on September 07, 2026, 07:23:53 pm »

Update. If reverb cables to and from tank and footswtch are removed amp works with and without tremelo just fine.

Using an RCA cable to a small amp the send side seems fine, the noise is coming from the return side.

Solved. The resistor running from the reverb pedal connector was soldered to ground lug but for some reason wasn't grounded. Ran a seperate ground wire for it and all seems fine.

Still don't uderstand where the bump in voltage came from and concerned it may be too high for lifespan of tubes and components...

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Tube Amp Building - Tweaks - Repairs / Re: Univox 202R Amplifier making noise

« Last post by astronomicum on September 07, 2026, 05:44:15 pm »

I had it for years. Can’t remember where I found this one. Have not gotten around to having it included in the library.

Trying to open the image, it is taking me to imgbb and it won’t open.

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Tube Amp Building - Tweaks - Repairs / Re: Univox 202R Amplifier making noise

« Last post by dbishopbliss on September 07, 2026, 04:58:53 pm »

Where did you find that schematic? I searched a lot of sites and could not find one.


Here's a picture of the amp internals. The curve is just lens distortion.

66

Tube Amp Building - Tweaks - Repairs / Tweed BluesMeister needs a tweak

« Last post by acheld on September 07, 2026, 03:52:17 pm »

Well now, more than a tweak.    I built this amp more than a year ago, but had to put it on the shelf.  I've recently started playing it, and I'm not so happy with it.

Problems:  1) This is a noisy amp.  When using only Stage 1, it's got a sort of ticking and a high frequency hiss when it is turned up past "4" on the volume dial.  When turned on, the Overdrive section (Tube 2) and/or the pre-amp boost just make this all the worse.  2) The overdrive section is not functioning as planned.

Today, I got off of my behind and put it on the bench. 

My question for today is in regard to the two scope images.  The test signal was input through the input jack at 30mV, with the OD section completely bypassed.  The images are taken from the output across an 8 ohm dummy load.

There is a clear notch in the waveform both on the way up and on the way down.  When I changed frequencies, I got a similar picture -- eg, this is not "noise" but unintended distortion.    Any ideas where or why this might be happening?   Initially I was thinking crossover distortion, but I don't think so.

Apologies in advance for the schematic, which I could not for the life of me fit on one page.   For the purposes of this particular question, the signal goes through page 1, skips page 2, and goes through the output section on page 3.

This amp was inspired by da Geezer, and Tubenit . . . 

67

Tube Amp Building - Tweaks - Repairs / Re: First amp build (5F1) would anyone mind double checking my turret board layout?

« Last post by HexEnduction on September 07, 2026, 03:17:50 pm »

don't forget the jumper 'tween the 2 8uF's grounds

Ah! I meant to go back and add the two jumpers at the top... I got so focused on double checking the components themselves that I completely overlooked them. I'll be adding them. I really appreciate it!

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Tube Amp Building - Tweaks - Repairs / Re: First amp build (5F1) would anyone mind double checking my turret board layout?

« Last post by shooter on September 07, 2026, 03:10:48 pm »

don't forget the jumper 'tween the 2 8uF's grounds

69

Tube Amp Building - Tweaks - Repairs / First amp build (5F1) would anyone mind double checking my turret board layout?

« Last post by HexEnduction on September 07, 2026, 02:48:38 pm »

Hi there, first time long time! I've built about a dozen pedals in the past year and I'm really excited to be jumping into the amp world. I'm working off the 5F1 Mojotone kit and I just finished up adding all of the turret board components (still need to solder/add the offboard wiring). I checked over my work a few times but I'm paranoid that I'm missing something or that I messed something up... if anyone would be so kind, could you take a look and let me know if this looks alright? Open to any suggestions or potential improvements as well.

A couple of things to note: I moved the 16uf cap furthest left up a bit on the board as otherwise it would cover up the mounting hole (the hole isn't visible in the picture I snapped)... I didn't want to have the cap sitting on top of a screw. I also pushed that blue 10K cap at the bottom left upwards a tad so that I can more easily solder the turrets without inadvertently burning the resistor. I tested each component before installing them, everything is looking good on that end.

Wiring diagram:



My board:


Thanks so much!

70

Tube Amp Building - Tweaks - Repairs / Re: Weber Princeton Reverb build - another problem after it’s been running great

« Last post by leevc5 on September 07, 2026, 01:25:14 pm »

With you folks help this thing was running beautifully. Suddenly a low freq oscillation has started. Sounds like the probe coming to earth to talk to the whales in Star Trek: the voyage home.

Along with the oscillation the voltage has gone up from rectifier tube to b4 first dropping resistor: was 386 VDV, now is 448 VDC. All the other voltages of course have gone up as well.

Replaced reverb return tube, replaced power tubes and rectifier = no change.
Went through the Rob Robinette light bulb start up sequence again and only change was to increase pin 5 6V6 voltage from -44 to -60. That did result in dropping the volume of oscillation a little but turning the reverb up increases the volume.

I’m guessing maybe something is wrong with the cap can but don’t know how to check that out.

As always, any suggestions greatly appreciated.