Need help deciding on my next amp build...

[deeder]

Give this one a look. It is a variation of the Marshall 18 watt...one heck of an amp. http://gerkules.16mb.com/tubeshematic/i ... te_TMB.jpg

Heyboer trannys, could you share what type of OT and PT ?

[labb]

Give me a day or two. I will have to get into my files and see. Know that I did not use Heyboer xformers.

[labb]

I used Magnetic Components Classictone transformers....290-0-290 volt, 120 ma for the power and approximately 8K primary for the OT. You could also match up at set of Hammond's for this amp. The Heyboer's are said to be reversed engineered from the originals but they are a little pricey for me.

[deeder]

I'm on the same page, Classic Tone 40-18056 PT seams to be right, THX ;^)

[chikov]

Give this one a look. It is a variation of the Marshall 18 watt...one heck of an amp. http://gerkules.16mb.com/tubeshematic/i ... te_TMB.jpg

Heyboer trannys, could you share what type of OT and PT ?

That schematic does look interesting and the transformer question was the one i was going to ask too .
I will do some research and keep you posted. Thank you.

[labb]

The type of rectifier you use will make a difference...I find that about 360 VDC is a good place to be for the Plate voltage of the EL84's

[deeder]

The type of rectifier you use will make a difference...I find that about 360 VDC is a good place to be for the Plate voltage of the EL84's

Good to know the result of your experiments, so it is the way to go.
Here is a great directrory I found on the path to my research : http://rh-tech.org/public/18-Watt/

[chikov]

The type of rectifier you use will make a difference...I find that about 360 VDC is a good place to be for the Plate voltage of the EL84's

Yes, your schematic starting to look very good. Would you call it "touch sensitive"? i do not need a lot of head room, I like a natural, organic overdrive any time of the day.
So, I will be getting this power transformer: http://www.classictone.net/40-18056.html
what about the output one? you said 8K primary... Let me look it up, see if I'll find something suitable on classic tone too.. BTW, will something like this work? -http://www.classictone.net/40-18037.pdf

[labb]

That is the OT that Classictone recommends for the 18 watt. It will be good. You can find several test of this amp on youtube if you do a search...You my want to take a look at the www.18watt.com forum. You have to be a member but all you have to do is sign up. It is simple. Zaphod_phil a moderator over there designed this amp. I call it a baby Plexi. Think that Marshall produced the original 18 watt that this is based on in the "70's. It is going to distort. It is a Marshall.

[chikov]

I pulled a plug and ordered a bunch of parts including the transformers to build the Baby Plexi EL84 amp. As I start wiring this thing I might be tempted to try PPIMV with it, although the amp has 2 volumes already

[chikov]

I just finished the amp and it sounds awesome. I must say it is the best sounding amp I built so far. It is super volume and touch sensitive and I finally getting overdrive sounds that i could get only out of my pedals before. I do have one question though. After running it for an hour or so, already twice my preamp tubes would start making scratchy, popping sounds. I would replace them and it would go away. Also i noticed that my filaments glow a little brighter than usual. When I measured my filament voltage it was 6.7 VAC. Is it normal or a little too high? If it is too high what is the best way to lower it to 6.3 V?

[pompeiisneaks]

I just finished the amp and it sounds awesome. I must say it is the best sounding amp I built so far. It is super volume and touch sensitive and I finally getting overdrive sounds that i could get only out of my pedals before. I do have one question though. After running it for an hour or so, already twice my preamp tubes would start making scratchy, popping sounds. I would replace them and it would go away. Also i noticed that my filaments glow a little brighter than usual. When I measured my filament voltage it was 6.7 VAC. Is it normal or a little too high? If it is too high what is the best way to lower it to 6.3 V?

filaments can take a decent amount. The rca datasheet shows 6.3V in parallel +/- 20% so max of 7.56V, there's also a max voltage that depends on the tubes, the rca one says the max heater negative with respect to cathode is 200V, so they can deal. it just shortens the life the more voltage you put on them. I doubt 6.7V is a problem

~Phil

[xtian]

Cathode followers can be rough on tubes. Check your plate to cathode voltage.

[chikov]

I have another design question. Does anyone know what is perpose of that 220k resistor, right after the stand by switch, between the first node and the ground?
PS, the scratchy sounds were coming from a bad connections in my preamp tubes’ sockets. Moral of this story - do not buy the cheapest ones with the little holes for 9 pins of the tubes.

[sluckey]

It's a bleeder resistor. The purpose is to quickly drain voltage from the filter caps when the amp is turned off.