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Old 09-18-2012, 08:20 PM   #1
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Join Date: Sep 2012
Hughes & Kettner Tubeman MKI tube replacement

Hi all,

I am new here and a novice guitar player playing a bit of Blues, Jazz, Classic Rock.

I had the opportunity to buy a H&K Tubeman MKI secondhand for 100 euros. I like some of the sounds I can get out of it a lot but the pedal lowers my guitar volume instead of giving me more gain. This happens on all three outputs (Guitar Amp/Mixer/Power Amp).

The controls work well, so I am thinking it is maybe the tube that needs to be replaced. The tube in it is a Electro Harmonics 12AX7 or ECC83. As I don't like the "Rock" setting (the pedal has four modes: Jazz/Funk/Blues/Rock)

I would like to have a smoother sound. Is a 12AT7 or 12AU7 as I read often on the internet a good replacement?

Will this solve my gain problem?

Last edited by kaouki : 09-18-2012 at 08:22 PM. Reason: Forgot to mention the problem was on all three outputs.
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Old 09-18-2012, 10:25 PM   #2
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Join Date: May 2006
Location: Oklahoma
I'm not too familiar with the pedal and can't find any schematics on it. If it is like a regular tube preamp (high voltage - not starved plate), avoid the 12AT7. It has very harsh distortion characteristics.

The tubes I would recommend you try to get are either the 5751 or a 12AY7. I don't know if this would make the pedal any louder since I can't find a schematic and certainly don't have one in front of me to test.
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Old 09-20-2012, 12:10 PM   #3
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Thank you for your reply. I'll try the 12AY7.

Here is a link to a schematic:
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Old 09-20-2012, 12:20 PM   #4
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Join Date: Sep 2012
When looking for the schematic I maybe found the answer. As Thomas Dunham stated on his Picassa gallery:
"The greatest tube pedal ever! The components are top notch except the pots which I have replaced twice already, otherwise very nice quality. Power supply is 12V A/C but when my power supply died, HK sold me a replacement 14V and threw in a set of said mini pots."
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