36W fired up finally!!!!

[Graydon]

Guys,

Actually, I fired it up on Monday but it was pretty pathetic. Today, I fixed some things after taking some voltage measurements and now it fires up and makes very nice sounds. I've played it through the normal channel with my PRS McCarty and it roars with far greater authority than the 18W but very similar character. So far, my observations are not really very indicative oof what I expect in the end because there is alot more work to do yet. Right now, the normal channel sounds great, but it is nothing but a lead machine. The V1 plate voltage is too low and it overdrives far too quickly. Also, the power tube bias voltage is a little too low so I need to increase that a little. With a few more tweaks, I think this is going to be a killer amp. It sounds great already.

I had Jeff do a little something extra special for the head cabinet on this amp, and I like it so much, I might adopt it for all my heads and do something else different for the 36W. Take a look...




You can download the high-res versions here...
http://www.gdsamps.com/Photo/36W/36WProto%20003med.jpg
http://www.gdsamps.com/Photo/36W/36WProto%20008med.jpg

I wanted something to set apart the 36W from the 18W head so in keeping with the "double" theme, I asked Jeff to do double piping and give it two brass vents. I might also make a special logo panel with a stylized 36W on it as well. We'll see. Gotta get it running first.

[Plexi]

Graydon.. looks great!! what no gut shot???
that is a bit different..

Richie

[Graydon]

Richie,

After I get a few things sorted out I'll post a gutshot. I don't want to mislead those that are building 36Ws with photos of an amp with wrong components in it. I've done that enough already.

[stevesuk]

Excellent Graydon, Is that two 18w output transformers or a choke and an OT ?
Steve UK

[Graydon]

Steve,

I used two 18W "Vintage" OTs. Believe it or not, I still haven't had a chance to try one of those in an 18W amp. They sound really good in this 36W though. Hopefully this week, I'll finish up another 18W and I'll A/B the two 18W OTs.

I plan to try using a choke in the 36W. I actually had one wired in for a short time when I was trying to find the source of the hissing sound in the power section. I thought maybe the big 1.5k resistor was causing the problem, bu it wasn't.

[stevesuk]

I am still stuck waiting for my Vox AC30 Output Transformer to arrive.
Now almost a month (not from Graydon I hasten to add).

The chassis and combo cab has been sitting here finished for weeks.

I am using Graydon's 36 W PT and that arrived with other bits within a week.

I am going to order another 30 watt OT from the UK supplier Bluebell Audio.
http://www.bluebellaudio.com/ who supply Hammond Transformers.

Even if the other one arrives first I have a suitable spare 50W PT for the next 36 Watt to pair it up with.

It looks like Hammond don't actually do a 4K 30 watt, but the 1645 looks pretty close, as Hammond trannies are not common in the Uk. Can anybody recommend which would be the most suitable Hammond 36 W Output Trannie ?

Steve UK

[Plexi]

Mines coming together,hopefully by next weekend,i'll have it done.
Got other amps here and an 18 to put together.. but the hard part is over,and now just the easy stuff. just takes more time to punch chassis,and figure it all out before starting..lol

Richie

[zaphod_phil]

I plan to try using a choke in the 36W. I actually had one wired in for a short time ...

I have a hunch that using a resistor(s) rather than a choke will help keep keep the essential feel of the Marshall 18W, even with a 36W design.

[zaphod_phil]

It looks like Hammond don't actually do a 4K 30 watt, but the 1645 looks pretty close, as Hammond trannies are not common in the Uk. Can anybody recommend which would be the most suitable Hammond 36 W Output Trannie ?

The November 2+2, which is a similar concept power amp-wise, uses the Hammond 1650N. You can readily get Hammond stuff from Onboard Electronics in ing, or from Bluebell Audio in Scotland. The latter are usually the cheaper...

[stevesuk]

Thanks Phil,
Do you think the 1650N which is 60 watt will give an 18 watt type sound as it won't be driven as hard ? although you are absolutely right about the 4.3K Impedance being the closest.
I'll give Bluebell a ring tomorrow and see what they have.

Steve Uk

[zaphod_phil]

Do you think the 1650N which is 60 watt will give an 18 watt type sound as it won't be driven as hard ? although you are absolutely right about the 4.3K Impedance being the closest.

Well, I think it's the closest compromise. IMO I don't think OT saturation plays much of a part in the 18W tone formula...

[Graydon]

I plan to try using a choke in the 36W. I actually had one wired in for a short time ...

I have a hunch that using a resistor(s) rather than a choke will help keep keep the essential feel of the Marshall 18W, even with a 36W design.

Phil,

You might be right here. I'll try it when I get a chance. I'll even try to hook up a switch so I can try it both ways. We'll see if that disruupts the voltages too much I guess.

I did a ton of work on the 100W with switches trying to find the best values for plate and cathode resistors. It is subtle sometimes and I found that my ears fatigued after a while so I had to do it in short spurts.

[stevesuk]

Phil.
I have ordered a Hammond 1650N and a 10H @ 100mA choke from Bluebell this morning.

I also received a JTM45 reissue choke from Marshall this morning, there isn't a value on it but the delivery note say's 1.2H Part No INDT-00013 Dagnall Electronics. I presume this means it is 1.2 Henries which is strange ? anybody know what a JTM45 reissue choke value is supposed to be ? I just assumed it would be OK for a 36 Watter. It was only £10 ($20)anyway so it doesn't really matter.

Steve UK

[dboul]

Congratulation Graydon! Any sound clips coming soon?

Very fun stuff! Thanks for sharing!

Dan