Bias test point....

[hesamadman]

Im wanting to add a bias test point on the outside of the chassis of a 2203 build. I am using insulated jacks. What I am assuming to do is to come off of any one of the 4 one ohm resistors/pin 8 of 6L6 to the jack? Ialso plan to add an additional jack straight to ground? I realize one could just touch the MM lead to the chassis but the jack gives a place to hold the lead.

[pompeiisneaks]

If you're going to do a bias point, you really need one per tube, or you could be setting it for the 'wrong' tube.  I.e. each time you put new tubes in, you'll get different conductance characteristics.  Then if you happened to set the bias at say 70% on that one, but all the others are quite hotter running tubes they could be all at 75 or 80% and burn up faster.  I don't know for sure what the average variance could be in current between tubes, but basically, it's a bit too much of a crap shoot.  Most people tap in the spot you're mentioning but one per tube.  (common ground should be fine).  That way you can ensure you're seeing the current on each tube and make sure that they're all within the range you're shooting for.

[Blind Lemon]

The way I would do it (at least the way your talking about) is to have 4 red bias jacks between the tubes and 1 ohm resistors (one for each tube) and have one black ground jack. Connect pins 8 and 1 on the power tube jack so you can run EL34, KT66/77 if you desire.

BL

[hesamadman]

That's a good point. I didn't think there could really be that much variance between them all but I guess you would want to check all 4 and average them.

[Blind Lemon]

At a minimum in pairs but best each one. 

BL

[hesamadman]

The more convenience in a tube amp the better

[frankenxtein]

How far away from tube could one expect to measure accurate voltages?
       So far everything I build is SE tiny point to point but , I have taken to using a tag strip to mount my bias resistor , next to the tube.

Would a second tag strip on the other side of the tube for B+ and Plate be a noise maker or lead to inaccurate readings?
The OP I'll assume is using a bot to dial in the bias. Me I'm wanting a safer place to place probes. Just ordered a better VOM with clips for the probes but , thought it worth mentioning. Just not so steady handed and these tiny tubes are hard to leave a spot to set the probes.

[Blind Lemon]

I don't really think you can really physically get them to far away inside an amp chassis. For the test points that the OP wants to install I am assuming (I know) the they would be on the back panel of the amp.  Look at some of the Hoffman boards and they are on the board. On some amps I only install the temporary to bias and then when the job is done pull them out.

As for probe tips I REALLY like the convenience of the Fluke Pincer or hook clips style tips. I had to look up the official name. We always just call them hooky-do's. Use a pair and you'll not know how you got anything done without them. I had 3 sets but am down to 1 1/2 now. I would be interest if anyone has a "less expensive" alternative.

BL

[frankenxtein]

I don't really think you can really physically get them to far away inside an amp chassis. For the test points that the OP wants to install I am assuming (I know) the they would be on the back panel of the amp.  Look at some of the Hoffman boards and they are on the board. On some amps I only install the temporary to bias and then when the job is done pull them out.

As for probe tips I REALLY like the convenience of the Fluke Pincer or hook clips style tips. I had to look up the official name. We always just call them hooky-do's. Use a pair and you'll not know how you got anything done without them. I had 3 sets but am down to 1 1/2 now. I would be interest if anyone has a "less expensive" alternative.

BL

Thank you. You can't get to far in one of these little boogers I've built. Routing and layering to keep noise down has been working for me. Just learning what is frivolous and expensive in building. "Switches are expensive" Got some orange hooky-do's on my cheap ESR for matching resistors and caps. My little Craftsman 82351 has no jacks and is past it's limit on some of these HT voltages. I fashioned some clips to go on the ends of them but , they don't stay put.
     I just ordered some cheap hooky-do's from a company I bought some cheap switches from  well $3.99 for 10  .... two of them might be good. They shipped those switches pretty fast lol. http://www.ebay.com/itm/401277068972?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT
To the OP ....... A small terminal block strip topside might be safe for test points , just thinking. With a cover I ordered some of those too from these same people they're long but I can cut them down where needed.