12004 Build with some general guidance

[YMI5150?]

I'll try to add some detail on this build for new guys. It wont include the little details but will include the overall work flow i used to get the job done. no sense in repeating reference shots and instructions George has already supplied. Hope this is helpful.

overall spec is the basic 12 series with a few personal value changes. trannies are from MM and added white knob pot to give external NFB tuning. All other parts sourced from Robert at Valvestorm.

I always start with the chassis mods before adding any components. Drill for the Larry grounds now if you're going that route. These trannies require new mounting holes so I drilled those out first as well. Put the face plates on and dremmel the holes now while its easy to clean up.

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mount the trannies and tube sockets. Some here believe the orientation of the OT is key to tone due to its magnetic field and proximity to other components so you may want to take note. wire up the bias resistors and heaters.

The boards can be done at any time and I was waiting on some parts to arrive. there are lots of references for this step.

moving on to the OT wiring. One key point is to measure impedance of the primaries to verify you've got the correct center tap. i've had incorrect wiring diagrams sent with trannies. measuring each lead to center should yield similar impedance. if its lopsided, you've got the wrong center. then wire the secondaries to the switch, and the output jacks. grounded this one per Larry Ground scheme. add the grid stoppers and the power tubes are wrapped up.

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Keep you posted.

[vanhalen5150]

What are those resistors there? I need to get back at my build this weekend.

[YMI5150?]

the 5.6ks? Allen Bradleys . not sure if they contribute to anything but they've been on the last few builds so keeping the ingredients the same.

[axeman]

To be honest with you, I know having swamp resistors on each pin 5 of the power tube sockets overall is better, but from my experience sharing 1 5.6k for two sockets gives you a certain tone that's closer to the original even 1.5k would be better. try to use 1/2 watt resistor as will. If you don't have any let my know, I have tons.

[Tone Slinger]

Cool thread Kev !

[YMI5150?]

alright, wrapped up the power section last night.

added power and standby switches and wired PT to them and the fuse holders. added the power filter board. a couple shots included for detail. used a 6VAC indicator. I think I like the 120 better. Sort of a bitch to get wires over to the heaters...
Note bias ground and screen filters grounded to lug 4. Main filters/rectifier grounded to lug 5.

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Time to move on to the main board next.

[vanhalen5150]

Riffa's on the screens? Can't see.....

I agree. The 6vac light is a pain to route over to the heaters.

[JimiJames]

...I agree. The 6vac light is a pain to route over to the heaters.

...I think I like the 120 better. Sort of a bitch to get wires over to the heaters...

yeah I've pondered these two options and I don't know what the difference is technically ?
Seems there's a reason other than being two separate dedicated voltage sources.
I like using the PITA way

[julkke]

I don't think it matters. I'd feel better using just 6v on the lamp instead of 120 but thats just me.

[YMI5150?]

sorry for the delay. just cant seem to stop drinking the iskra/piher kool aid. got a handful from Italy and we're back in business. $125 is worth it, right?! i wired up the underside of the board while waiting on the components.

populate the board and start attaching wires to the chassis (used Larry ground scheme in this case), as neatly as possible. hit those ground lugs with some power to get good ground contact.

a few shots of the underside of the board, input jacks, and a shot of the board dropped in. a few more hours wiring up preamp tube socekts, input jacks, and tone pots and it'll be time to power up.

this gives you an idea of work flow. again, details are all over this forum.

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[Strat78]

Nice work, I wish I could start all my builds from scratch now. Yeah, our cup runneth over with iskras these days. The problem with the French seller's Iskra's are that most are the later production and have short leads. The guy from the UK has all the early resistors and he is practically giving them away. Is that a classic tone PT?

[vanhalen5150]

Who are guys getting resistors from? ebay?

[YMI5150?]

Low voltage tonepros PT from MM.
Shannon-one of the bay sellers is out of Italy. Name is Alberto. I message him with the entire list and tell him to fulfill with either brand. He sent me the entire build that was mixed for $125 us including shipping. Good guy too.

[vanhalen5150]

Low voltage tonepros PT from MM.
Shannon-one of the bay sellers is out of Italy. Name is Alberto. I message him with the entire list and tell him to fulfill with either brand. He sent me the entire build that was mixed for $125 us including shipping. Good guy too.

Wow...$125! I currently have a full set of phif's and almost a full set of Iskras. I think I just need a few odd values of the Iskras. Those are for future builds though. I don't even want to know the total value I've paid for those.

[vanhalen5150]

Did you get that big round board cap in the preamp from him? Alberto!