Update on my 36W power section values

Post by **Graydon** » Wed 03/24/04 12:00 pm

Guys,

I was going to respond to Steve's thread but I figured that this would be a more general update so I started a new thread.

I did some more tweaking last night on my 36W. I made some very good progress too.

First of all, it is important to know that I am using a two diode half wave rectifier with a 125ohm "sag" resistor to provide the B+ off the 290-0-290 winding from the PT.

Also, I am still running a pair of my new "Vintage" 18W output transformers in parallel. I have yet to try out the new 36W OT that I had made by Heyboer.

I ended up changing the cathode resistor on the EL84s to a single 100ohm resistor for all 4 EL84s (again, like the AC30 but with 100ohms instead of 50). This got me right around 12V at the cathode. I also played with the second dropping resistor in the power supply rail. That would be R6 (8.2k) which I replaced with a 1.5k resistor. That brought all of my B+ voltages on all of the tubes to within a few volts of stock 18W values.

I found a stupid misteak on my TMB channel and fixed that and now my 36W works perfectly well in nearly every regard. I played it for about an hour at various settings and levels. I compared it to my latest couple 18W heads through a couple different cabinets and I compared it to my first Dumble-clone.

The verdict?

I love it. It has tremendous sustain, great touch response, and a monstrous overdrive tone that is like the 18W tone but bigger. It does have a little more clean headroom. This wasn't immediately noticeable but after playing for a while, searching for clean tones, I had the amp set to around 2 on the volume and I was getting some really sweet clean tones. Then I plugged back into the 18W at the same volume level and the same playing style, and the tone was full of distortion.

I'm taking it down to Dearborn tonight for Josh Smith to check out. He's on a minitour with Ricky Fante who is releasing his first big album with Virgin Records net month. Anyone know Josh? He lives in Florida now I think. If anyone in the Detroit area wants to join me, I'll be at the Border's Books store in Dearborn this evening.

Post by **Graydon** » Sat 03/27/04 7:17 am

Here is a photo of the power section of my new 36W. If you download the hi-res photo, you should be able to see the detail pretty well.

Hi-res here... http://www.gdsamps.com/Photo/36W/36Wproto%20011med.jpg

danelectro · Post by **danelectro** » Sat 03/27/04 12:40 pm

that looks great. hrmm i really wann try this thing out

Retro · Post by **Retro** » Fri 01/28/05 2:13 pm

I'm fairly new at this and could use a shove in the right direction

. I've been looking at the November project Rev 8 schematic but R6 doesn't seem to match up with the second dropping resistor that Graydon refers to. Can anyone point me to the right schematic?

Post by **zaphod_phil** » Fri 01/28/05 4:08 pm

The November schematics won't correspond to this. Look at the regular or TMB 18W schematics (in the downloads section) and just imagine an extra pair of EL84s, as well as two OTs in parallel....

Post by **Plexi** » Fri 01/28/05 5:12 pm

Graydon.. looks very nice.. isn't your TMB a little different,or is it like the one we have here or similar? Sometimes useing different rectos etc,you have to play with the values of stages to get the sweet spot voltages.
Sometimes it can make an amp sound,and work or react better,than compared to a different design.

Also as Phil said,the November is close,but still its not the same,and will work and sound a bit different. There are a couple things that keep them and many other amps from being the same.

Graydon, Jaysg asked me about the 36 watter in another thread..compared to the 18. I think they both have there on place to be used. But I really like the 36..as does SteveUK.. I guess untill a few people have built one,and can compare them,then they will know. The 36 watter really works well for band situation,where sometimes the 18 might not have the extra poop. I like the head version..use a 4x12 for loud..and a 2x12 for a bit less. But not a bedroom amp..lol
I've played the 36 head against an AC-30,,i know they are different amps, but the 36 watter smoked it. At least it did for what i like..

Richie

SpinCycl · Post by **SpinCycl** » Sun 01/30/05 7:17 pm

zaphod_phil wrote:The November schematics won't correspond to this. Look at the regular or TMB 18W schematics (in the downloads section) and just imagine an extra pair of EL84s, as well as two OTs in parallel....

Why use 2 OT's in parallel?

mightymike · Post by **mightymike** » Sun 02/13/05 9:26 am

Transformers in Parrallel add Wattage. So if you have (2) 18 watt Output Trannys in Parrallel you end up with 36 watt. I'm guessing he probably used the double 18watt trannys as a tonal reference point to compare the different OTs he's considering using in his ever evolving kit. As long as there's room on the chassis you can use both I guess, my only concern would be hum and $$.

Plexi wrote: I've played the 36 head against an AC-30,,i know they are different amps, but the 36 watter smoked it. At least it did for what i like..

Richie

Is that 36 head the one that you used to make the RICH AMP clips? If yes, Did that amp have the AC30 OT? If no, which OT trannys did you use in each?

Post by **Plexi** » Sun 02/13/05 11:14 am

"""Is that 36 head the one that you used to make the RICH AMP clips? If yes, Did that amp have the AC30 OT? If no, which OT trannys did you use in each?"""

Yes it was the Rich Amp.. and it used Heyboers smaller AC-30 set of trannys..
The OT and PT have been upgraded..the PT is now 290-0-290
And the OT is modeled after the 18 in the way it is made, but it is a stand up mount..and 35 watts..

I posted a while back about a band that used this amp on there CD..its in the final mix,and will be out late Spring early summer for release..
You'll be able to hear the things this amp can do..that my files didn't capture..

Richie

bnwitt · Post by **bnwitt** » Sun 02/13/05 11:54 am

So when are we going to get some schematics and/or layout drawings on this version?
Barry

Post by **Plexi** » Sun 02/13/05 12:17 pm

Barry the updated version was posted somewhere..i'll have to swap it in my gallery with the other one i had.
But the layout is here.. except the cap can is mounted on the end of the chassis..and the PT is not through the chassis like is shown on the layout.
http://www.18watt.com/files/36wboard251104.jpg
I think he did it like this to show the wiring better..

Richie

bnwitt · Post by **bnwitt** » Sun 02/13/05 2:11 pm

Richie,
thanks for that info.
Barry

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