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Details about  Alnicomagnet "Blues Harp" Mod Kit Epiphone Valve Junior V.3 and Head

Alnicomagnet "Blues Harp" Mod Kit Epiphone Valve Junior V.3 and Head

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Item location:
Rochdale, Lancashire, United Kingdom
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Last updated on  18 Feb, 2015 15:47:26 GMT  View all revisions
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Item specifics

New: A brand-new, unused, unopened and undamaged item in original retail packaging (where packaging is ... Read moreabout the condition
Type: mod kit
Model: EVJ V.3 Blues Harp Brand: alnicomagnet


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Hi and welcome to this listing for my "Blues Harp" mod kit for a V.3 (version 3) Epiphone Valve Junior 5W Class A Combo or Head amp (black circuit board and 14 digit serial numbers).

This mod kit is specifically for the V.3 Epiphone Valve Junior Combo or Head ONLY.

It is NOT suitable for V.1 or V.2 Epiphone Valve Juniors, nor the Harley Benton GA5. I supply other kits for these amps, (see my other listings).

The V.3 is improved over the V.2 and V.1 amps. It has corrected input impedance (1megohm), 12AX7 preamp tube biased to Fender spec, output transformer with a 5K2 primary winding, and 3 output jacks (4R, 8R and 16R loads) for both head AND combo amps.

As a result, it is much better sounding straight out of the box.

However, the B+ (HT) voltage is still way too high, resulting in a too high anode dissipation for the EL84 output valve. There's still no Standby Switch, nor HT fuse. And the circuit still needs tweaking in a number of areas to bring out the potential of these amps.

Mods available:

1. Drop HT voltage to a safer level.

2. Fit extra HT filtering to further reduce ripple (hum).

3. Fit HT fuseholder and fuse.

4. Re-bias pre-amp tube to my "Blues Harp" spec

5. Change interstage resistive network to clean up sound (reduce noise pickup).

6. Fit Standby switch.

7. Fit Pentode/Triode switch

8. Fit Line-out jack with built in ground lift.

9. Fit Mallory 150M coupling capacitors.


Instructions and pictures are kept in a folder. The folder is stored on a download site. You will receive a download link via email which will be sent to you at the same time as you receive confirmation from eBay that the kit has been shipped. I will use your PayPal registered email address unless you inform me of an alternative preferred email address. If you don't receive the link, please check your spam filter/junk folder, or contact me directly (alnicomagnet@hotmail.co.uk).

You will need a pdf reader to access the instructions. You will need a picture viewer to view the pictures.

Your amp can feature some or all of my latest prototyped and fully tested mods
Some of them in more detail:
  • HT voltage: the stock amp still has a much too high HT voltage. This results in the EL84 output valve being worked too hard. Designed working voltage (anode to cathode) is 250V. Maximum voltage is 300V. I measured 316V anode to cathode. My mod reduces this to around 300V. What's more, the absolute maximum anode (plate) dissipation for an EL84 is 12 watts. I measured and calculated 12.6 watts. Clearly too high. This can result in a burnt out valve, or shortened valve life at the very least. My mod reduces anode dissipation to around 11 watts. You can now use your NOS Mullard safe in the knowledge that you won't destroy it!
  • Standby Switch - absolutely essential in my opinion. All valve amps (especially those with silicon rectifiers) should have a standby switch. It allows the valves to become fully warmed up before applying the HT (high tension) (high voltage) to the valves. Eliminates cathode stripping and other damage. With proper use of the Standby Switch (wait at least 30 seconds before switching on, and switch to standby before switching off the mains power switch) your valves should last at least twice as long! NOTE: anode to chassis voltage surged to 389VDC on switch-on, before dropping back to 326V as the valve warmed up and started to conduct, yikes!
  • HT Fuse: let's take a look at the protection for the Valve Junior. The mains lead itself is protected by a 5amp fuse. The mains input to the amp (mains transformer primary winding) is protected by a T1AL 250V time delay (slo blo) fuse. The heater (filament) supply is protected by a T4AL 250V fuse. That leaves the HT winding (with no protection)! Imagine if the output valve is damaged by vibration and shorts out. Or, what if a power supply capacitor blows or shorts - voila! there goes your expensive mains transformer! For the sake of a few quid it ain't worth the risk!
  • Pentode/Triode Mode selector switch. A rather elegant way of reducing the output power from 5watts (pentode) to 2watts (triode). Triode mode also produces a mellower tone with a different distortion character.
  • Line-Out Jack with built-in ground lift. Rather than take the line-out signal from the pre-amp output, I decided to take the signal after the output transformer, thus giving it the true output valve distortion sound. Now there is no need to mic up at a gig, simply run a lead from the line-out jack to the mixer desk, or into a more powerful amp, with no more worries over microphone feedback. 

Check out Mat Walklate playing various harmonicas through three different microphones into a Harley Benton GA5H head into a Harley Benton G112 speaker cabinet. (The GA5H is very similar to the old V.2 Epi Valve Junior, but has an "EQ" control).


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Item location: Rochdale, Lancashire, United Kingdom
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