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Dirty-South Blues Harp forum: wail on! >
Alnicomagnet Mod Kits
Alnicomagnet Mod Kits
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sammyharp
108 posts
Mar 28, 2011
12:05 AM
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I just finished installing a mod kit from Alnicomagnet in my Fender Champ 600. Wow! I'm really impressed with the difference. It eliminated the hum issues of this amp. There's barely any audible hum any more, even when the volume is at max. The tone is way better! The kit I ordered was the Blues Harp mod. The modifications included in the kit are:
-amp revoiced to original 5F1 voicing
-Tone Stack replaced by an enormous Srague Orange Drop capacitor.
-Added a standby switch
-Added a pentode/triode switch
and 3 mods for hum reduction:
-AC to DC heater (filament) supply conversion mod
-HT supply filter and voltage drop mod (adjust the voltage for longer tube life and less hum)
-Repositioning the output transformer
I highly recommend this kit. The CD that came with it had full instructions and photos of all the mmods, as well a specs and schematics for numerous amps, various speakers and tubes, and tons of other info. The instructions are very clear and easy to follow, even for someone like me who has limited electronics knowledge. As far as I know, Alnicomagnet has kits for several different amps. The kits are available on Ebay. Again, I'm very impressed with the results. If you're looking for an easy to follow mod kit, this is the one to get!
Last Edited by on Mar 28, 2011 12:06 AM
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Stevelegh
109 posts
Mar 28, 2011
12:53 AM
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I want to get one of these, but I've always been scared off by having to drain the filler caps on tube amps. I don't want to die!!!
How easy is all this to do? How long does it take to mod the amp in total?
My previous soldering skills are limited to putting new pickups in guitars.
I've got a Champion 600, but was thinking I'd rather just buy a stock VHT Special 6, which will be cheaper if I screw the Champ up.
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sammyharp
109 posts
Mar 28, 2011
2:14 AM
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Draining the caps isn't so hard. Here's how I do it: play a sustained chord through the amp, and turn it off, then all the way up while holding the chord. Hold it until the sound dies completely. I then drained the caps completely with my multimeter set to 200V (I live in Germany). The Mutimeter read about 14 volts when I started the draining, and I drained it until it was around 2. According to alnicomagnet, anything under 10 volts is fine.
The mods vary in level. About half of them involve just replacing parts, cutting and resoldering wires, and drilling a few holes. 2 of them (HT filter voltage drop & pentode/triode switch) actually involved altering the printed circuit board, wich requires some fine motor skills. It involves drilling through the trace (the "wires" printed on the board) and cutting through the trace to split the signal. I did the mods from easiest to hardest, so I built up the confidence for the difficult ones by the end.
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Stevelegh
111 posts
Mar 28, 2011
4:36 AM
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OK, all this sounds quite doable for me.
Ebay time!
Thanks
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5F6H
587 posts
Mar 28, 2011
4:36 AM
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@ SteveLegh: "I want to get one of these, but I've always been scared off by having to drain the filler caps on tube amps. I don't want to die!!!"
What I do is clip a jumper wire, with crocodile clips at both ends, one end to the chassis ground, the other end to pin 1 or pin 6 (plate) of a 12A#7 tube socket. This gently drains the caps in under a minute, all the time the jumper is there they cannot charge back up & you have a visual safety check. Remove the jumper before powering up.
Sammyharp's method works too. On big Fenders like Super Reverbs, Twin Reverbs & RI Bassmans (NOT original bassmans, or some reproductionss & brown & blond tolex amps that have not been rewired - visually check first), where the first filter cap after the rectifier is made up of 2 caps in series, each bypassed by a resistor, throwing the standby into "Play" mode, with the amp unplugged from the wall AC, drains the caps.
Last Edited by on Mar 28, 2011 8:57 AM
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Greg Heumann
1092 posts
Mar 28, 2011
7:50 AM
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Both Sammy's and 5F6H's approaches to draining the caps only work if the circuit is working properly and all tubes are installed. This is NOT always a safe assumption! If you are working on an amp it isn't a bad idea when you power it back up to do so slowly. Some people use a Variac. I don't have one, but I do start with NO tubes to ensure the transformer is working properly. Then just the rectifier tube to ensure DC voltages are appropriate, etc. At this stage there is NOTHING to drain the caps at power off but a lot of time. The only way to be sure is to short across the caps. I simply use a pair of needle nose pliers with insulated handles. If you can't get the tips of your pliers across, hook a nice heavy test lead to ground, and then using your insulated handle pliers, maneuver the other end of the lead to the positive side of each cap. If energy is left, you'll get a nice big spark and a big "SNAP" noise to go with it. Personally, I like this excitement!
Again -you might have made a mistake. Forgot to connect something, whatever. I think the only truly safe way to discharge the caps is to know you've shorted across each one.
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/Greg
Last Edited by on Mar 28, 2011 7:52 AM
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5F6H
588 posts
Mar 28, 2011
8:57 AM
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No tubes need to be installed for the jumper wire from plate to ground method, or the standby method for totem pole wired, series main filters. You do need to check that the plate resistor that the jumper wire connects to is not open (if you heard the amp work before opening it up, chances are it isn't), by checking resistance from pin 1 or 6 (no tube installed), accross the plate resistor, back to the B+ rail.
Caps can recharge themselves after being discharged, which is why i like the jumper method, as long as you can see it's there, you know you are safe, no surprises.
Last Edited by on Mar 28, 2011 8:58 AM
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tmf714
574 posts
Mar 28, 2011
9:07 AM
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You should also install a 470 ohm resistor in the jumper as well-1st end always to ground.
Pin 1 wont work on all tubes- like 6eu7- as it's a heater pin. To be super safe,always use a volt meter.
Last Edited by on Mar 28, 2011 9:08 AM
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5F6H
589 posts
Mar 28, 2011
9:51 AM
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When bleeding caps from the plates of a preamp tube, you already have the plate resistor (can be from 47,000 ohms to 470,000, most commonly 100,000 or 220,000) itelf between the B+ rail & ground, the jumper wire itself is sufficient.
Good call on the 6EU7, indeed, always be sure which pin is the plate (if other than a 12A#7/12DW7/5751)when using this method, also be sure that the plate in question is being utilised, some amps leave an unused half of a preamp tube unconnected, obviously this method won't work on the unconnected pins.
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tmf714
575 posts
Mar 28, 2011
10:00 AM
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The resisitor simply stops the arcing and sparking created by inadvertent contact.
Also extremley important to always keep one hand behind your back-only one hand in the amp at all times.
Last Edited by on Mar 28, 2011 10:04 AM
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Stevelegh
113 posts
Mar 28, 2011
12:35 PM
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@Greg Heumann:
'If energy is left, you'll get a nice big spark and a big "SNAP" noise to go with it. Personally, I like this excitement!'
You're a fu**ing child! Very funny!
I'll take your 'Big Bang' advice. Thanks all. I'll ask the wife to post up on here if I don't survive....
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Matzen
116 posts
Mar 28, 2011
12:40 PM
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Anyone do the VHT mod yet?
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