New 45/100 Build - Odd V3 readings

Traviswalk · Post by **Traviswalk** » Sat Apr 02, 2011 3:02 pm

Hey folks, just wrapped up a new 45/100 build and have some odd voltages on pin 2 and pin 7 of V3. They are coming in around 16-17 when George's voltage chart says they should be in the 30 range. I tried to resolder to remedy any cold joints but still putting out the same reading. Amp fires up well, very quiet and sounds great! Here are some pics to help.

I'm using the Metro OT and PT.

I'm trying to post pics but it keeps saying the file size is too big despite shrinking them?!?

Traviswalk · Post by **Traviswalk** » Sat Apr 02, 2011 3:09 pm

Here are some pics:

Traviswalk · Post by **Traviswalk** » Sat Apr 02, 2011 3:11 pm

Traviswalk · Post by **Traviswalk** » Sat Apr 02, 2011 3:21 pm

Traviswalk · Post by **Traviswalk** » Sat Apr 02, 2011 3:22 pm

toner · Post by **toner** » Sat Apr 02, 2011 4:58 pm

Some meters have trouble with the PI grid readings. This may be your issue. See SDM's reply here: http://forum.metroamp.com/viewtopic.php?f=4&t=29426" onclick="window.open(this.href);return false;

Traviswalk · Post by **Traviswalk** » Sat Apr 02, 2011 5:03 pm

toner wrote:Some meters have trouble with the PI grid readings. This may be your issue. See SDM's reply here: http://forum.metroamp.com/viewtopic.php?f=4&t=29426" onclick="window.open(this.href);return false;

Thanks, funny enough I just came across that post! Another q, the amp sounds great, but playing it next to a Marshall Hendrix Super 100JH and the 45/100 build is much quieter. The bias checks out fine and my CompuBias says that each KT66 is putting out ~17 watts, any potential areas to look at for an overall quieter amp than expected? No noises, no squeel, wonderful tone, just quieter.

toner · Post by **toner** » Sat Apr 02, 2011 5:15 pm

If it were extremely quiet I'd check the PI cathode resistor but yours looks correct (470, not 470k). How much volume difference is there between the amps?

Traviswalk wrote:No noises, no squeel, wonderful tone, just quieter.

This may be a blessing in disguise.

Traviswalk · Post by **Traviswalk** » Sat Apr 02, 2011 11:00 pm

I think I know what's throwing me off. The PEC pots I used I believe are linear pots whereas I'm sure the Super 100JH are audio. The new 45/100 build gets the proper super freakin loud, but I've got to get to the later 50% of the volume pots before it opens up. The Super 100JH is loud right off the bat but doesn't do much on the back part of the dial.

Does that sound reasonable?

Traviswalk · Post by **Traviswalk** » Sat Apr 02, 2011 11:06 pm

Traviswalk wrote:I think I know what's throwing me off. The PEC pots I used I believe are linear pots whereas I'm sure the Super 100JH are audio. The new 45/100 build gets the proper super freakin loud, but I've got to get to the later 50% of the volume pots before it opens up. The Super 100JH is loud right off the bat but doesn't do much on the back part of the dial.

Does that sound reasonable?

Strike that, the PECs on the volumes are audio, do you think it's the quality of the PEC pots?

toner · Post by **toner** » Sun Apr 03, 2011 12:38 am

Does the 100JH have a bright cap? I don't think they do but a large bright cap would explain the volume pot behavior (getting loud early on the dial).

shakti · Post by **shakti** » Tue Apr 05, 2011 3:34 pm

Very nice build! I'm not quite sure why you're getting that reading. Did you measure the resistors prior to soldering? Also, that 470R is soldered on a turret with three other resistors, which I always have trouble with. Make sure you've got a good contact there.

I'm not sure if you're saying the amp isn't as loud as the 100JH, or whether it just reacts differently on the dial? At full tilt, is it still less loud than the 100JH?

shakti · Post by **shakti** » Tue Apr 05, 2011 3:36 pm

BTW, I'm lazy....I usually just solder up everything, check voltages on the plates and screens of the output tubes as well as bias, and as long as I'm sure everything else is connected where it's supposed to, I never bother to take voltage readings on the preamp tubes. It either works and sounds right, or it doesn't...

Traviswalk · Post by **Traviswalk** » Tue Apr 05, 2011 5:30 pm

shakti wrote:Very nice build! I'm not quite sure why you're getting that reading. Did you measure the resistors prior to soldering? Also, that 470R is soldered on a turret with three other resistors, which I always have trouble with. Make sure you've got a good contact there.

I'm not sure if you're saying the amp isn't as loud as the 100JH, or whether it just reacts differently on the dial? At full tilt, is it still less loud than the 100JH?

Thanks! I did measure all resistors prior to soldering, they all checked out within their % parameters, so feel pretty good there. I will recheck that turret with three resistors, that was a challenging one.

As for the volume compared with the 100JH, the new 45/100 does get as loud when cranked, but not as much roar as immediately as the 100JH. And perhaps total volume is less than the Marshall, maybe 20%. The volume build is much more manageable and usable early on the volume dials (

) I suppose I shouldn't complain about it!

shakti · Post by **shakti** » Wed Apr 06, 2011 1:26 am

Does your amp have 1k or 470R screen grid resistors? IIIRC, the 100JH has 470. That could explain it maybe?

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New 45/100 Build - Odd V3 readings

New 45/100 Build - Odd V3 readings

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