Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Snake5150 on October 15, 2024, 05:55:49 pm
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Would it be possible (and or fruitful) to test my amp build without the board installed and put 20-50 vac on the power section via a variac and test the tube sockets etc to make sure I’m getting power thru the transformer and at the sockets?
If I were to put voltage into the transformer let’s say 20vac what should I expect on the secondary side? It’s a pacific audio magnetics 45w jtm style transformer.
Also as far as master volume. What size shielded 2 conductor cable would suffice 18g, 20 g?
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before power, with ALL tubes out;
Ohm each tap on the PS chain to ground. You want numbers >50,000 ohms, counting up fast, typically to infinity on the meter
If that's good;
use a gator-clip, "short out" the 1st tap at the cap / Resistor junction, so Jump cap + side to chassis, clip your meter to those same 2 points, verify it's < 10 ohms, then un-jump the gatorclip and it should "react" the same as the 1st test.
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before power, with ALL tubes out;
Ohm each tap on the PS chain to ground. You want numbers >50,000 ohms, counting up fast, typically to infinity on the meter
If that's good;
use a gator-clip, "short out" the 1st tap at the cap / Resistor junction, so Jump cap + side to chassis, clip your meter to those same 2 points, verify it's < 10 ohms, then un-jump the gatorclip and it should "react" the same as the 1st test.
I’m deff gonna need some clarification for this one. “Ps chain to ground” is ???
Basically want high resistance for one test and low for the other?
Just need some help with what points you’re referring to for the test.
Also I appreciate the help and understanding as I am a newb.
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Do you have a light bulb limiter?
And know how and when to use it?
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I’m deff gonna need some clarification for this one. “Ps chain to ground” is ???
Power supply B+ filter cap chain. The B+ filter caps are daisy chained together, filter cap/dropping R/filter cap/dropping R, etc.
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Do you have a light bulb limiter?
And know how and when to use it?
I have a variac and built a light bulb limiter. To my understanding it consumes current so that a fault isn’t enough current to hurt the equipment.
I was looking to test the amp before putting in the board and making its connection. Then using the variac and limiter to startup fully
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I have a variac and built a light bulb limiter. To my understanding it consumes current so that a fault isn’t enough current to hurt the equipment.
Ok, good and yes to protect against shorts. Bulb lights up, and stays liter, shut it down!
I was looking to test the amp before putting in the board and making its connection. Then using the variac and limiter to startup fully.
Yes, I read that in your OP.
I would just build the amp, most guys do, then fire it up with the light bulb limiter, 6v6 amp 60w bulb, 6L6/EL34 amp, 100w bulb.
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I have a variac and built a light bulb limiter. To my understanding it consumes current so that a fault isn’t enough current to hurt the equipment.
Ok, good and yes to protect against shorts. Bulb lights up, and stays liter, shut it down!
I was looking to test the amp before putting in the board and making its connection. Then using the variac and limiter to startup fully.
Yes, I read that in your OP.
I would just build the amp, most guys do, then fire it up with the light bulb limiter, 6v6 amp 60w bulb, 6L6/EL34 amp, 100w bulb.
As long as it’s an incandescent bulb it doesn’t matter right. I have a lot of spare 100 and 150 reptile heat bulbs. They are just light bulbs with colored glass.
I was going to refer to rob rinettes startup procedure. I thought it was well written.
https://robrobinette.com/Tube_Amp_Startup.htm
I’m still looking for an answer on the Mv cable. 18,20g?
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It is possible to build the power supply first without making connections to the board.
Wire all the heaters to the tube sockets.
Make all the power transformer connections including the rectifier, on/off, fuse, pilot light and filter cap power rail.
Just don't make the connections to PI and preamp, etc.
The lightbulb limiter is very useful.
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I would just build the amp, most guys do, then fire it up with the light bulb limiter, 6v6 amp 60w bulb, 6L6/EL34 amp, 100w bulb.
As long as it’s an incandescent bulb it doesn’t matter right. I have a lot of spare 100 and 150 reptile heat bulbs. They are just light bulbs with colored glass.
It does matter. Yes it has to an incandescent, a halogen will work too.
But the lower the wattage to more it will protect the test piece. It's filament will have more resistance.
On a single ended Champ type amp, 1 x 6V6, I use a little 40w bulb. :icon_biggrin:
That 150w, probably could use it for a 4 x 6L6/EL34 amp. Or a 6 x power tube amp.
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You need a good, correct schematic AND layout drawing to use this. It works great;
https://el34world.com/Forum/index.php?topic=17701.msg178630#msg178630
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Lots of posts on wire size. Most charts for in chassis wiring lists 11 amps for 20 ga., 7 amps for 22ga. That all I remember. Volume control you could probably use 24 ga. or smaller. I use RG 174 shielded to wire grids if shielding needed. It is 25 ga.
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I think you guys have read Sluckey state he changed his shielded cable installs to RG316 because the insulation of the center conductor is teflon and doesn't melt during soldering. It is really good stuff however it isn't as flexible as RG174.