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 Post subject: Valveking 212 and 100 schematic and replacing preamp tubes?
PostPosted: Sat Jan 08, 2011 9:39 am 
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Hello Forumites,
I've been reading topics in this forum for quite a while and it has been really helpful. I've been playing guitar for about 25 years and have played Peavey amps most of the time. I started with a Bandit 65 then went to a Triumph 60. I now have a VK212 that has been converted to a head (I didn't convert it, I bought it like that). I'm using the VK speakers in a custom 212 closed back cab lade by Saxon Cabs. I play a 1985 Horizon II Custom that I've had since new. It is my only electric currently and I really like it. I've played it almost every day for the last 25 years and it still is as soli as when I bought it.

I have a question about the placement of the preamp tubes in the 212. The schematic I found for the head seems to be opposite to the actual tube placement in the 212 based, as far as I can tell based on where v3 sits in relation to the power tubes. Is this correct, v1 is in the corner behind the transformer, v2 is beside it, behind v3 and v3 is beside the power tubes? I've seen in the manual that the 212 and 100's knobs and jacks are opposite of each other.
I changed the preamp tubes last night with this thinking in mind and wanted to make sure this was correct.

Here's what I went with in preamp tubes:
Position V1 Clean TungSol 12AX7 Re-Issue
Position V2 Overdrive JJ ECC803S Large Plate
Position V3 Phase Inverter Sovtek 12AX7LPS

One more question, I also bought new power tubes and have unplugged the amp with the standby on to drain the caps. How long do I need to wait for them to drain? I've read that it can take up to 24 hours.

I went with Tung-Sol 6L6GC-STR's for the power tubes.

Thanks, this forum has been extremely helpful so far.


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 Post subject: Re: Valveking 212 and 100 schematic and replacing preamp tubes?
PostPosted: Sat Jan 08, 2011 9:55 am 
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V1 close to guitar input jack.

V2 in the middle.

V3 close to power tubes.

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 Post subject: Re: Valveking 212 and 100 schematic and replacing preamp tubes?
PostPosted: Sat Jan 08, 2011 11:14 am 
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Excellent, thanks.

Any thoughts about the power tubes and draining the caps? I looked at the wikimod about leaving the standby on and unplugging the amp to drain them and wanted to make sure that this was correct before I replace them.


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 Post subject: Re: Valveking 212 and 100 schematic and replacing preamp tubes?
PostPosted: Sat Jan 08, 2011 11:23 am 
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you wont come in contact with any current while changing power tube any more than you did with the preamp tubes. unless they break while putting them in anyway. ive never discharged caps when changing tubes. i kinda doubt anyone else here has either unless they had another reason to do so.

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 Post subject: Re: Valveking 212 and 100 schematic and replacing preamp tubes?
PostPosted: Sat Jan 08, 2011 1:20 pm 
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Play it safe by unplugging amp when you do tube exchanges.


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 Post subject: Re: Valveking 212 and 100 schematic and replacing preamp tubes?
PostPosted: Sat Jan 08, 2011 6:37 pm 
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Thanks for the info. I'll make sure that the amp is unplugged when I change the power tubes.


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 Post subject: Re: Valveking 212 and 100 schematic and replacing preamp tubes?
PostPosted: Sun Jan 09, 2011 3:47 pm 
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Tubes are changed without incident. All is working fine.

Thanks for the assistance.


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 Post subject: Re: Valveking 212 and 100 schematic and replacing preamp tubes?
PostPosted: Sun Jan 09, 2011 4:17 pm 
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Without incident is the best way to change tubes. Uh Huh Oh Yeah :wink:


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 Post subject: Re: Valveking 212 and 100 schematic and replacing preamp tubes?
PostPosted: Sun Jan 09, 2011 9:33 pm 
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BTW the knobs and jacks are "opposite" between the combo and the head because the combo chassis is inverted (tubes would fall out of the sockets if there was no retention force). iirc the preamp board layout is exactly the same.

If the switches were mounted to a circuit board like the pots and jacks, they would operate "backwards" (up = OFF). Thankfully they are hardwired...

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 Post subject: Re: Valveking 212 and 100 schematic and replacing preamp tubes?
PostPosted: Mon Jan 10, 2011 6:53 am 
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Horizon2 wrote:
Thanks for the info. I'll make sure that the amp is unplugged when I change the power tubes.

The only reason it is suggested to turn off the amp(not just in standby) is to allow the rather hot envelopes to cool enough for you to handle the tubes. It is best to use some type of insulation to pull them anyway because skin oil left on a tube, if the tube is run really hot, lead to the glass cracking. The hotter the tube envelope to more of a risk.
Negative bias comes up first so you can hot swap tubes with no ill-effects, even with the amp out of standby. Receiving tubes and small power tubes have a controlled time delay for heating the filaments to full emission, 7 seconds. That means the tube is not conducting immediately, but gradually increases conduction over that time. After 7-10 second, the amp should be fully ready to apply full signal through it.

Were the old pre-amp tubes defective? I noticed you put in a new "Tung-Sol" tube. Unfortunately the name was sold to New Sensor who stamps the highly regarded Tung-Sol brand name on any sort of tubes they can get(they also acquired the name of "Mullard", and "Svetlana" with no connection to their former quality either, essentially the same as Yugo acquiring the name Ferrari and stamping it on their cars). Do not be confused but the slight of hand, real Tung-Sol tubes are in very short supply, usually in a boarded up old TV repair shop or industrial parts department of a plant somewhere.

Small tubes, called Receiving Tubes, such as the 12AX7 , were designed to last many years unless physically damaged. Power tubes do consume themselves over time but small receiving tubes might need replacing every 10-20 years in a head and 7-15 years in a combo where they are subjected to more vibration abuse. I have some test instruments, HP RF precision signal generator built in 1968 that still has all original tubes and maintains calibration, it is on for most of the day every day since it was new. My old McIntosh tube preamp built before that still has all original tubes and still meets spec in all parameters.

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 Post subject: Re: Valveking 212 and 100 schematic and replacing preamp tubes?
PostPosted: Mon Jan 10, 2011 8:31 am 
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I had purchased the amp about 6 months ago used and am the 3rd owner as far as I know. I wasn't thrilled with the clean and distortion sounds I was getting and after checking the tubes and finding them stock, I was waiting for an opportunity to change them. The amp was acting a bit funny last week, really fizzy low volume from the distortion channel from time to time so I figured it was time to change all the tubes.

After reading a lot in this forum, I made my tube selection from advise posted here.

I have to say I like the clean channel a lot more and am still dialing in the distortion channel as I'm not quite there with it yet.

I can say for sure that the stock speakers seem to have come to life in the clean channel after the tube change. I need more time with the distortion channel before I can say for sure if I like it better.


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 Post subject: Re: Valveking 212 and 100 schematic and replacing preamp tubes?
PostPosted: Mon Jan 10, 2011 9:34 am 
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Horizon2 wrote:
Hello Forumites,

One more question, I also bought new power tubes and have unplugged the amp with the standby on to drain the caps. How long do I need to wait for them to drain? I've read that it can take up to 24 hours.

I went with Tung-Sol 6L6GC-STR's for the power tubes.

Thanks, this forum has been extremely helpful so far.


The best way I know is to place the amp in a normal play mode and unplug it while playing. keep strumming until it completely dies. Leave the power switch on to ensure any residual capacitor charges do not build up (chemical reaction inside the capacitor similar to a battery) while you have your hands inside the amp. The whole process should only take a few minutes, buy the time the tubes cool you will be safe.

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