ValveKing "JCM" mode using Volume Boost switch

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CharlieP
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Re: ValveKing "JCM" mode using Volume Boost switch

Post by CharlieP » Mon Jun 24, 2013 1:04 pm

Always good to re-check your work! :wink:
Charlie
Gib LP Robot 2008 Met. Red, , 5E3 Build 2014
Fend Tele Dlx2010 SPL ED w/Tron Tune
3rd Build 6G3 Br. Deluxe Head 2018
VK 112 Web OT Rotary Swit. Bias Mod
Gret. G2622 P90s,G2655T, G5034, Pro Jet, Epi WildKat 2019

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65 SG
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Re: ValveKing "JCM" mode using Volume Boost switch

Post by 65 SG » Mon Jun 24, 2013 5:07 pm

Maybe that's why we're still waiting for the new VK series amps?? :o

filter...broken...I may have a form of Tourette syndrome

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CharlieP
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Re: ValveKing "JCM" mode using Volume Boost switch

Post by CharlieP » Mon Jun 24, 2013 10:04 pm

65 SG wrote:Maybe that's why we're still waiting for the new VK series amps?? :o

filter...broken...I may have a form of Tourette syndrome
Last minute check! :lol:
Charlie
Gib LP Robot 2008 Met. Red, , 5E3 Build 2014
Fend Tele Dlx2010 SPL ED w/Tron Tune
3rd Build 6G3 Br. Deluxe Head 2018
VK 112 Web OT Rotary Swit. Bias Mod
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Jonhy_Greenwood
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Re: ValveKing "JCM" mode using Volume Boost switch

Post by Jonhy_Greenwood » Mon Jul 22, 2013 7:42 am

Hi! I perform this mod, but not tried the amp yet.
I realize that the clean channel now have an additional path to ground. Maybe this could down the signal strengh before getting the PI.
The additional path is the R107 (now 750k) plus the series other 750K resistor. Besides the 1M resistor "R111" it still is there..
Could the clean channel varied something with this mod?

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Re: ValveKing "JCM" mode using Volume Boost switch

Post by recklessrog » Thu Nov 07, 2013 6:28 am

I have now carried out this mod PLUS my master volume control mod and bias/equalisation mod to seven valveking amps, two of which were the 100w version (VK212) So far, everyone has been blown away with it, by combining this mod with the master vol mod and using germanium diodes for D101-D102 gives infinite control and the ability to have a really pumped in your face sound without excessive volume. Ideal for practicing at home (no more "turn that frickin noise down"!! from the misses!!!!! :lol: )
Incidentally, running bias at around 38ma for the O/P tubes seems to be about optimum for most makes of tube. My only real criticism of the original Ruby tubes is that they are poorly matched, but the Bias/Balance mod I listed easily compensates for this and can make even a very badly matched pair sound good. An example was one amp I modified had one tube drawing 32ma and the other 68ma and the amp sounded S**t. After adding my balance mod and setting the bias to 38ma per tube it sounded great!
Remember that if the output stage is way off you will be chasing your tail to get a decent sound. Do the Bias/balance mod FIRST, Listen to the clean channel and make sure that it is "clean" then worry about the overdrive channel.
Have fun everyone :D

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Re: ValveKing "JCM" mode using Volume Boost switch

Post by aaronsg71 » Thu Aug 28, 2014 12:20 am

Sry this thread is a year inactive now but I have the 100 watt head and what do I do to make my amp like the JCM800? Do I cut some diode out? Thx

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Re: ValveKing "JCM" mode using Volume Boost switch

Post by CharlieP » Thu Aug 28, 2014 11:51 am

aaronsg71 wrote:Sry this thread is a year inactive now but I have the 100 watt head and what do I do to make my amp like the JCM800? Do I cut some diode out? Thx
Start by reading from the beginning. 65sg covers it pretty well. There is no need to rehash what has already been posted. Very good pictures of what he has done.
Charlie
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Re: ValveKing "JCM" mode using Volume Boost switch

Post by Crwilsn » Tue Jan 06, 2015 1:29 pm

I know this is an older thread. It wanted to ask a question about the jcm mod. The stock vk tone is too harsh for anything I play. Both this and the mod on the wiki site use a switch to turn the mod on and off. I play mostly classic (late 60s through 80s) rock with a bit of 90s alternative occasionally. Has anyone wired this permanently on?

By my reading, I can

cut out c117 completely for the brightness

pull the left lead of R107 closest to the tube socket. Use a piece of heat shrink to isolate the resister still attached by the right leg.

Jumper the now empty r107 terminal to j94

Now the amp is permanently in jcm mode, right?

Thanks in advance for any assistance on this.

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Re: ValveKing "JCM" mode using Volume Boost switch

Post by BowerR64 » Fri Feb 12, 2016 3:02 am

I picked up a cheap VK112 on my local craigslist for $80. needed new power tubes but that wasnt to bad.

I did the mod but i have nothing when i push in the volume button on the dirty channel. The gain button seems to work altering from the VK to the JCM mode but what should the volume button do? Or is it no longer used?

I didnt have a 750K resistor either but i did find a 470K i used the 750K from the last lug on the switch to the JP61 jumper wire. Then i used the 470K from the last 2 lugs jumped across.

I think i did everything right sept the correct value of resistors.

Also i notice that the 2 modes have different gain levels, when in VK mode the gain seems really low and subtle more of a crunch. Then when in the JCM mode the gain is almost double the level. I would almost prefer the 2 be the oposite. Slightly more gain in the VK mode and slightly less in the JCM mode. Maybe this is the resistor values?

What should the volume button do now after the JCM mod?

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Re: ValveKing "JCM" mode using Volume Boost switch

Post by BowerR64 » Fri Feb 12, 2016 6:23 am

Never mind i figured it out, i had one of the leads from the switch going to JP60 instead of JP94 like its suppose to.

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Re: ValveKing "JCM" mode using Volume Boost switch

Post by BowerR64 » Sat Feb 13, 2016 9:19 pm

I replaced all 3 preamp tubes with 12AT7/ECC81 tubes and now its a classic rock machine!

The 12AT7/ECC81 tubes have 60% of the gain of the 12AX7 so you have alot more sweep of the gain knob

IMO this amp needs a larger reverb tank, its to tight IMO and the reverb isnt smooth enough.

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Re: ValveKing "JCM" mode using Volume Boost switch

Post by torcamaniac » Thu Nov 03, 2016 12:14 pm

Hi guys.

Just did this MOD to my Valveking 112. Have a question though.
If I understood correctly, the amp is in JCM mode when the Volume button is not pressed, and in VK mode when the volume button is pressed?
When I don't press the button the sound has less distortion and is louder and more fat.
When I press it the sound is more distorted and quieter and thinner.
Judging from this I suppose I'am right or?

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Re: ValveKing "JCM" mode using Volume Boost switch

Post by Lil git » Wed Feb 22, 2017 5:28 pm

Hey guys,
I've done this mod on my vk212 and everything works perfectly except for a popping noise when I either switch between channels using the footswitch, or toggle between jcm and vk mode using the volume gain button. I've also done the channel switching delay beforehand and was working fine before this jcm mod so I'm assuming this is where the problem is.
Any ideas would be appreciated. Thanks!

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Re: ValveKing "JCM" mode using Volume Boost switch

Post by psycom » Fri Feb 24, 2017 3:27 am

I recall reading something about the value of the resistor used that is causing your popping. OH... Look under the "switching Delay Fix" or soemthing like that. You'll find it there.

I too just picked up a VK100 Head and am reading and note taking like mad. It's the ultimate tweaker project thanks to some seriously talented folks that have shared their knowledge. THANK YOU GUYS! SERIOUSLY!!

All I've done so far is put a GE 5 Star 12AX7A in V1, A JAN PHILLIPS 5751 in V2 and a 12AX7EH (Eletro Harmonix) as the PI in V3 and honestly only did that to use the tube as I hate those thigs and thought it might be okay there and it actually has been but then it was made in 2009 too. It had one of those in the V2 position but was thicker glass like the industrial Sovteks. I couldn't pull it out for the life of me so ended up removing the can around the tube so I could get a grip on it. Ended up taking all the cans off as I'm rolling lots of tubes and those get in my way. It sounded horrible too. Squealed like nobodies business and piercingly bright. In V3 it doesn't have that affect. I believe it's a different EH tube also.

You really "should" use the covers as they do help in RF rejection. Can't say much for cooling and certainly not holding them in. Definitely use care and a rounded rocking motion to pull them up and out. The pin gap goes dead ahead straight forward so once you have the tube in hand and get the feel for the position as it will seat a tad once in the correct spot I found some mighty force with a little rocking action will get 'em seated. You can feel it go in on mine.

Always wanted a 100 watt head. Now I want the 25/50/100 watt switch as 100 watts is retardedly hurtful. That's made for a large stage. Outside I'd say. I paired it up with some really high efficient speakers from my buddy Jason Tice at PMR Speakers. Whoa...a 200 watt head. LOL Love it as long as long as I'm wireless and far away. Seriously Check his speakers out. I have about 7 video's up under his name on YouTube demoing them or trying to destroy em. You'll hear what I mean. The mans a genius.http://www.pmrspeakers.com .... tell 'him Richard sent you and he'll take good care of you. Been working together since 98.

Peace. Oh... get some rel Power tubes. The Sovteks GTX+ when matched sound pretty damn good. Stay away from JJ's all around. And Electro Harmonix. Buy all the JAN Phillips 5781's? 51's (they have both 5881' and 12ax7wa's and if you can't afford RCA Comando's or GE 5 Star or any other USA NOS tube the Sovteks seem to have teir shit togethet. I just picked up quads of unlabled but gret sounding "Mesa Boogie 420" for 30 bucks shipped. ALL matched and sound great. Almost a perfect match for the fake 5881 Internationals' I bought for 125 shipped. Lots of thievery going on in the relabeling of tubes. Read up and ONLY buy in USA. To return with tracking and signature which is required cost $85 for a single GZ34 off eBay. They helped me but still. What you buy from China stays here god or bad. Look at it that way.

Richard

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Re: ValveKing "JCM" mode using Volume Boost switch

Post by Lil git » Fri Feb 24, 2017 3:05 pm

Thanks for the reply, Richard. I had done the switch delay mod and was successful at getting rid of the delay without any popping when switching between channels. However, when I did the "jcm mod using the volume boost switch" i got this pop when switching modes. I should say it happens only when I am in jcm mode (volume boost not engaged) and switching between channels. I should also add that instead of the two 750k resistors it called for, I used 1m resistors. I'm wondering if that is what's causing me grief.
Anyway, I'm kind of a hack and I do enjoy the how-to's posted by these knowledgeable forum members. So thank you, thank you, thank you!

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