Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: jordan86 on May 24, 2020, 11:43:33 pm
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Just finished building my first amp. Princeton Reverb. Have yet to fire it up, but noticed something odd as I was finishing my filaments. I decided to start at v1 and work my way back, making sure I kept pins 9 connected and pins 4/5 connected down the line, not mixing the two up. Continued that on to pins 2 and 7 on the 6v6's. Continuity was correct and the two lines did not mix. As I connect them to my pilot light connections, I now get continuity across all the filament pins on every tube.
Is that correct? At first I thought I mixed them up at the pilot light. Seemed illogical, but I flipped the wires at the pilot light to see if that changes anything. No change.
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What is "continuity"?
Depends on the meter. Often "under 100 Ohms".
What is the Ohms of a heater? Looks like 6V at 0.3 Amps. Which is 20 Ohms. (It is not quite that simple.)
Even if you don't have tubes in. The PT heater winding Ohms has to be much less than the Ohms of all the heaters in parallel. So probably under 1 Ohm. "Continuity."
So your observation is expected.
And continuity is for trailer-light technicians. Read the numbers.
> the two lines did not mix
Makes no difference if they do. The several tubes are doing all different things at all different signal levels and gains. There can not be any "cancellation". Yes, the two or four Power tubes do the same thing/levels, but at such high levels that heater AC does not matter.
If you feel better seeing heaters "right", then be happy. (Two wire colors might be a lot faster than beeping every connection.)
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". As I connect them to my pilot light connections, I now get continuity across all the filament pins on every tube."
-Jordan86
Normal . You read pilot light's heater.
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I have a similar situation with my build - '65 Blackface DR that has me scratching my head. I thought I would piggy back on this post since it seems to be similar conditions.
The output transformer has "wire continuity" across the black and green secondary (~0.7 ohms). When adding those to the two-speaker output jack circuitry, where wire continuity is correct as it relates to tip and sleeve separation, I now get total wire continuity (beeps) in the entire output jack circuit. I now have wire continuity between the ground, tip, switch and chassis, with a 1/4" plug in place. Is the circuit still correct? (This is my first build... and post)
BTW: I have checked the OT separately - no wire continuity the OT frame or chassis.
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A 4Ohm secondary reads about 1-2 Ohms and one side is connected to ground, so you not neccessarily made a mistake. I think it is very satisfying to draw again by just looking at what you built and confirm that it is done right.
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I have a similar situation with my build - '65 Blackface DR that has me scratching my head. I thought I would piggy back on this post since it seems to be similar conditions.
The output transformer has "wire continuity" across the black and green secondary (~0.7 ohms). When adding those to the two-speaker output jack circuitry, where wire continuity is correct as it relates to tip and sleeve separation, I now get total wire continuity (beeps) in the entire output jack circuit. I now have wire continuity between the ground, tip, switch and chassis, with a 1/4" plug in place. Is the circuit still correct? (This is my first build... and post)
BTW: I have checked the OT separately - no wire continuity the OT frame or chassis.
The OT secondary is a single piece of wire, so Yes, there should be DC-continuity between the ends of the wire
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not clear on what you're asking;
if there is nothing plugged into the speaker jack and you're using a 12A, it will be shorted zero ohms
when you plug in a 1/4" (connected to nothing) you will get small ohms tip to ring, because you're measuring "across" the OT secondary.
IF the 1/4" is connected to speaker you now have the speaker in parallel with the OT secondary and you should read small ohms
get used to using a meter without BEEPS, know how to "zero" the leads so you get a better reading in the small ohm range