Superlite TMB Schematic Voltages

[crgfrench]

I like the Dale CMF-60 resistors -- 500V and they are 1/2W at 125 degrees C rising to 1W at 70 degrees. And metal film is the quietest resistor material (with the exception of wirewounds). Plus they are 1% tolerance.

Of course in that spot I agree with Josh -- Brown Devils all day.

[JMPGuitars]

Just a thought on resistor voltage rating---If you start really checking the voltage rating of resistors and where they are used in the circuit you will be alarmed. Most 1/2 watt resistors are rated for around 300 volt. Same thing with wire. What voltage rated wire do you use..Most use 300 volt wire for the whole amp...Thousands of amps have been built with 1/2 watt resistors and wire that do not really meet the voltage rating where they are use in the circuit..For resistor worry about watt rating more than voltage rating..But, then me, I use nothing less than 1 watt rated resistors and 600 volt wire..

Really? I haven't seen any 20AWG less than 600 volt, and that's what's most common. But if you try and read the tiny writing, you'll see that the actual voltage rating also depends on other variables. The wire I use says it's either 600V or 1000V. That could be based on wattage, or temperature, or simple identity crisis. Who knows.

The 1/2 watt Xicon carbon films are rated at 350V. Those are what I normally use, but I'm trying out some 1W MF in my next build that are rated at 500V.

Out of the typical 18 watt builds, the only resistor that comes close to 350V is the 220K discharge resistor for the filter caps. The next closest is 225V at the PI, and that's being dropped from around 290 or 280 from "C" at the plate resistors. That being the magic point to put in magic carbon comp resistors, the half watters of those are also usually at least 350V. So either way, pretty well covered.

Thanks,
Josh

[mac dillard]

I think that UL 1007 covers 300 volt wire either stranded or solid and that UL 1015 covers 600 volt wire either stranded or solid. Both are available..As to the resistors, What voltage does an 18 watt amp B+ go to when you fire the amp up for test with no tubes.

The MF's are said to be quieter than the CF but I have had no noise problems in my amps using the CF's.. Have you tried any of the teflon/PTFE wire?

[crgfrench]

Yes I've been using this and I love it.
https://tubedepot.com/products/20-ga-si ... -ptfe-wire

[JMPGuitars]

I think that UL 1007 covers 300 volt wire either stranded or solid and that UL 1015 covers 600 volt wire either stranded or solid. Both are available..As to the resistors, What voltage does an 18 watt amp B+ go to when you fire the amp up for test with no tubes.

The MF's are said to be quieter than the CF but I have had no noise problems in my amps using the CF's.. Have you tried any of the teflon/PTFE wire?

Wires meet multiple UL standards at different temperatures. The wire I just looked at says 1015/1230 at 105C for 600V. It also says 1032 90C 1000V. Before that it says 1013/1233 or something like that. It's hard to read...especially this early in the morning.

Unloaded voltages do go higher, but the filter caps should be using higher rated wirewounds anyway. Personally I don't turn on amps unloaded. I have a variac, and don't do unloaded testing.

I like PTFE wire, but I don't always use it. It has a higher temp rating than most others, and doesn't melt as easily (including compared to what I listed above). Whether or not you want to use silver plated wire is a different story, subject to different opinions. Personally I have used the silver plated stuff, but a lot of people think it's not needed for guitar amps, and also the silver plating can rust if exposed. Whether or not that will happen in practice is a different story. Don't spill soda in your amp.

[Riffmonster]

Hey guys,

I did not wanna open a new thread for this cause it is kinda the same topic.

If I want to build the Superlite tmb, can't I just aim for the voltages of the lite 2b? I wanna build the Superlite tmb with tube rectification, so I would take the same power section of the lite 2b and just add the 27k 2 watt resistor to get node D. Is there anything wrong about going that way? I can't really see why it should. Thanks!

[Daviedawg]

Yes you can. All 18 watts which aim for the 18 watt tone will have similar voltages at key points.

Dd

[JMPGuitars]

Hey guys,

I did not wanna open a new thread for this cause it is kinda the same topic.

If I want to build the Superlite tmb, can't I just aim for the voltages of the lite 2b? I wanna build the Superlite tmb with tube rectification, so I would take the same power section of the lite 2b and just add the 27k 2 watt resistor to get node D. Is there anything wrong about going that way? I can't really see why it should. Thanks!

Yeah, like Dd said, they're mostly the same. If you look in the downloads section you'll see my Lite 2/Superlite TMB voltages use the same sheet. viewtopic.php?f=25&t=24418

Tube rectified or solid state, you still want the same B+.

Thanks,
Josh

[Riffmonster]

Thanks Josh, can't wait to build it!

[kinmike]

So I used a 130 ohm, 12 watt resistor and got the B+ down to 343 volts at 120 vac. Pin 3 of power tubes is 11.48. Are these close enough or do I keep chasing it?

Thanks,

Mike

[JMPGuitars]

So I used a 130 ohm, 12 watt resistor and got the B+ down to 343 volts at 120 vac. Pin 3 of power tubes is 11.48. Are these close enough or do I keep chasing it?

B+ is great, leave it there. Now you should get your Pin 3 (cathode) voltage up to 12V. What's your cathode resistor now?

Thanks,
Josh

[kinmike]

Josh,

Well, being impatient, since my last post and seeing your last post I went from 180 to 220 on the cathode resistor. The voltage at pin 3 of the power tubes is now 12.48 but the B+ went up to 352.

Maybe I need two decade boxes to get this straight. Looks like another week is needed for me to order more parts. I guess I need to order multiples in the range of each resistor. I see you suggested that already.

Mike

[JMPGuitars]

Well, being impatient, since my last post and seeing your last post I went from 180 to 220 on the cathode resistor. The voltage at pin 3 of the power tubes is now 12.48 but the B+ went up to 352.

Do you have two 100 ohm 5W or higher resistors? You can put them in series at Pin 3 and see what voltages you get.

Thanks,
Josh

[geoff 1965]

006.JPG

i made this little test box Mike,it's 2 wirewound variable resistors "colvern" and it's been one of the most useful test pieces i've got!
i used it for the sag resistor,adjusting B+,el84 biasing and fine tuning voltage dividers.
you simply patch it in and adjust it till you get the exact voltage you want then remove it and measure the resistance.
with a 150R bias resistor i had exactly 12V on pin 3 but my dissipation was just over 12 watts so i've got 180R now with 12.7V on pin 3 and dissipation of 11.5 watts and to be honest both values sounded just as good.

[kinmike]

Do you have two 100 ohm 5W or higher resistors? You can put them in series at Pin 3 and see what voltages you get.

Thanks,
Josh

I actually had the wherewithal to order a 200R 5 watt resistor last time. I installed it, but with the 130 ohm dropping resistor my B+ is still 356. Pin 3 was 12.3v.

Dang, I was hoping to get this solved.

Mike

[kinmike]

006.JPG
i made this little test box Mike,it's 2 wirewound variable resistors "colvern" and it's been one of the most useful test pieces i've got!
i used it for the sag resistor,adjusting B+,el84 biasing and fine tuning voltage dividers.
you simply patch it in and adjust it till you get the exact voltage you want then remove it and measure the resistance.
with a 150R bias resistor i had exactly 12V on pin 3 but my dissipation was just over 12 watts so i've got 180R now with 12.7V on pin 3 and dissipation of 11.5 watts and to be honest both values sounded just as good.

Yeah, looks like I could use something like that.....

[JMPGuitars]

I actually had the wherewithal to order a 200R 5 watt resistor last time. I installed it, but with the 130 ohm dropping resistor my B+ is still 356. Pin 3 was 12.3v.

Dang, I was hoping to get this solved.

Mike

Throw that 200R in place to drop the B+. Put a 180R on the cathode and check your voltages.

Please also post a photo of how you have it setup.

Thanks,
Josh

[kinmike]

OK, I put the 200 ohm in with a 180 ohm cathode resistor and my B+ is 340 with 11.4 volts on pin 3.

I assume I need to still get closer to 12 volts. Back to 200 on there as well?

I know I need to change out the 5 watter to 10 later on.

Thanks,

Mike

[JMPGuitars]

OK, I put the 200 ohm in with a 180 ohm cathode resistor and my B+ is 340 with 11.4 volts on pin 3.

I assume I need to still get closer to 12 volts. Back to 200 on there as well?

I know I need to change out the 5 watter to 10 later on.

Thanks,

Mike

Yeah, give it a shot and see what happens. 11.4 isn't terrible, but if you can get it closer to 12 it would be better on your tubes. The truth is plenty of people have their 18 watters biased there or hotter, but it's not ideal.

TBH 5W is fine there too, 10W is overkill. That's why people often use 10W there (for overkill). I think the minimum for the voltage you're dropping is around 1.5W, so 5W is pretty safe for now. 10W is better because it shouldn't get as hot (assuming the 5W actually gets hot).

Thanks,
Josh

[kinmike]

Ended up using 220 ohm 5 watt for the dropping resistor and 200 ohm for the cathode resistor. B+ is 337 and pin 3 of power tubes is 11.6.

I could probably try 220 for the cathode to get a little closer but that is another Mouser order.

Mike