18Watt.com

Bieworm wrote: ↑

Wed 06/30/21 5:56 am

thanks Jack... but I'm not going that route anymore. I've convinced the man the best way to go is the 18 watt. I'm going to do some testing with the different secondary taps to see if that is a better alternative for attenuating things. The only concern is the tremolo operation at lower voltages.. but since tremolo isn't that important to him it's no disaster if it don't wiggle at lower B+ settings.
OTOH I could look into the mosfet IRF840 system that the toneking has. That tremolo is pretty darn good too...
Lots to think about for now.. even been thinking about building him a superlite TMB with reverb for that matter

I'll be interested to see how this all works out. I'm interested in building a lower power amp when my current hi-fi projects are done, and the list of possible features is pretty long. I have a lot of tubes on hand, so almost any combination of pentodes and triodes in nearly any configuration is possible. I'm leaning toward push-pull triodes after hearing your 1W amp, but that's just one of the many decisions that have to be made. It probably won't be a TMB-style, because I'm not very enthusiastic regarding the limited tonal variation available with this type of tone stack. It's a must for re-creating the sound of the early Marshalls, but otherwise not necessarily the best for my purpose, especially now that I have the 36W.

Please post your progress on this project so I can steal as many of your ideas as possible.

Jack

Ok.. problem!!
Just wanted to order those transformers...turns out Ampmaker is on holiday until september...
But thinking on... theoretically I could use half of the winding of a 300-0-300V secondary and rectify that to get 212V instead of 350V, right? A full wave rectifier of course. Is it then absurd to make that switchable from full winding to half, given I switch off the amp to do that?
BTW, it's gonna be the superlite TMB reverb

The red notation is mine...




Jack

That’s a cool idea Jack!
Personally I would opt for Vvr on the power & phase section,the customer will have more scope i.e. he can dial in full power for headroom or lower power for breakup.at half power you are stuck with the tone/breakup of that voltage.
decisions decisions Bieworm!

geoff 1965 wrote: ↑

Thu 07/01/21 1:58 pm

That’s a cool idea Jack!
Personally I would opt for Vvr on the power & phase section,the customer will have more scope i.e. he can dial in full power for headroom or lower power for breakup.at half power you are stuck with the tone/breakup of that voltage.
decisions decisions Bieworm!

You're right Geoff. You've done that before. Have any good schematic and tips of doos n don'ts ?

The schematic is in the downloads section Bieworm,the spec for the mosfet is a NTE2377 which is n-channel,900V,8 amp,150W dissipation,TO-3P type.they are hard to find and expensive but the Toshiba 2SK2968 is very close in spec,there are others as well if you search.
Needs to be bolted to the chassis with silicon heat transfer pad insulating between,you can get that in 100 x 100 x 2 mm sheets on eBay.
You can adjust the minimum voltage with the resistor to ground from the 1M pot,100K gives you roughly 10% of max i.e. 350V max voltage will be around 35V.i upped it to 220K on my amp so minimum voltage was around 60V but you can experiment with that yourself.
I did draw out a layout somewhere if I find it I will post ithttps://www.18watt.com/files/18_watt_liteiib_vvr_pa_pi_141.gif
Also if you use a dual axial electrolytic after the can cap you add the filtering to the preamp that is cut out i.e.the first half of the dual can filters the vvr & preamp,the second half filters post vvr to the power & phase section.

Well, I only posted that as a solution to Bieworm's question about using half the winding. This technique provides half voltage, but it doesn't cut the available power in half like using half the winding. It's a better option than using half the transformer, regardless of the purpose for doing that. You might want to keep it in mind in case you ever need half-voltage for a preamp/driver stage, but don't want to waste so much power and heat across dropping resistors.

Jack

That method is definitely going in the build notes Jack,I actually had the transformer Bieworm was planning to use and to be honest the half power option just gave a little earlier breakup,the tone was the same as full and it was just as loud!
the vvr gives you more scope and lower volume to play with.

And this one? https://www.tube-town.net/ttstore/kit-t ... lator.html

The dissipation and drain are a lot lower on that mosfet Bieworm @ 75W & 4.5 amp,suitable for just the screen voltage but are you going to be the guinea pig that tries it out?

geoff 1965 wrote: ↑

Thu 07/01/21 11:34 pm

The dissipation and drain are a lot lower on that mosfet Bieworm @ 75W & 4.5 amp,suitable for just the screen voltage but are you going to be the guinea pig that tries it out?

Naahh.. I'm going to build one myself. I found a 800V 5A N channel mosfet that look more interesting..
https://datasheetspdf.com/mobile/919474 ... or/P5N80/1
Only problem is a well priced pot. The max wattage for a good price over here are 0.5W cts pots.. is that ok?

The schematic shows 1/2W which are rated at 500VDC so that will be okay, “build one yourself” as in the VoCo screen voltage?

No I'm going the safe path and use stuff from you guys

Okay Bieworm then the mosfet has to be close to the type & specs I posted earlier,notice the 1M pot is linear as well.

geoff 1965 wrote: ↑

Fri 07/02/21 1:54 pm

Okay Bieworm then the mosfet has to be close to the type & specs I posted earlier,notice the 1M pot is linear as well.

Do you reckon the 800V 5A 140W mosfet isn't sufficient?

The others are at least 8amp,plus you have to check the gate,drain & source are the same configuration.i used a 2SK2698 which was 500V,15amp,150W by default”I got the 69 wrong should have been 96 when ordering” it works but i’m going to change to a 900V 8Amp when I build the new chassis for the 6V6 amp.
here's the spec sheet for the NTE2377

geoff 1965 wrote: ↑

Fri 07/02/21 5:29 pm

The others are at least 8amp,plus you have to check the gate,drain & source are the same configuration.i used a 2SK2698 which was 500V,15amp,150W by default”I got the 69 wrong should have been 96 when ordering” it works but i’m going to change to a 900V 8Amp when I build the new chassis for the 6V6 amp.
here's the spec sheet for the NTE2377
nte2377.pdf

Hey Geoff.. I'm a novice to mosfets. But this one seems to be able do pull it off?

Not sure Bieworm,i’m no expert on mosfets myself,I stayed close to the NTE2377 specs when I got mine i.e. TO-3P type

Josh, is the extra triode from the tremolo TMB going to make a big difference compared to the SL TMB? I mean, is the SL TMB going to sound fat enough?

Bieworm wrote: ↑

Sun 07/04/21 4:27 am

Josh, is the extra triode from the tremolo TMB going to make a big difference compared to the SL TMB? I mean, is the SL TMB going to sound fat enough?

How fat it sounds depends on your build. Use the latest docs, the latest docs are the best.

Here's a couple I made in the past (18 and 36W versions):

https://www.youtube.com/watch?v=PeRZXThV54s

https://www.youtube.com/watch?v=UZ1X5SdKnLc

https://www.youtube.com/watch?v=EB0gux3Wrdk

Thanks,
Josh