Marshall 18 watt

[jeff]

 I'm thinking of building my brother a marshall 18 Watt for Christmas. I know he's been interested in that amp for a while. I noticed that the first two gain stages are parallel. Is it ok to run the firts tube into the second instead of parallel or would that be too much gain. The high output would go to the low input so it would be like having the gain on 10.

 I'm thinking of building all the neseccary circuitry to do that onto the board but unused. Send it to him stock. After he's had the amp for a while I could send him instructions on how to mod it if he wanted to(move this wire here, that wire there). Nice little time bomb

 He knows enough about amps I know he could do it. I think that'd be a cool suprise for him and a neat project.

Do you think I should keep the tone knob before the PI or between the first two stages?

[Fresh_Start]

Jeff - there's an entire forum dedicated to the 18 Watt:
http://www.18watt.com/index.php
Of course, it's down right now.  Also, I didn't find it to be the friendliest place on the web but others must.

There's also the Trinity Amps 18 Watt forum:
http://www.trinityamps.com/phpbb/viewforum.php?f=7&sid=c1bba4b9bd88aee913ad46eae156673a
Excellent atmosphere and very helpful.  The "S-III" variant is interesting to me, but there are lots out there.  You have to register and log in to see the schematics & layouts for everything:
http://www.trinityamps.com/phpbb/viewforum.php?f=12
REALLY good documentation IMHO.

Don't forget Doug's 18-Watt Stout!  You can even add reverb if you want to.

Cheers,

Chip

[jeff]

I could add an extra 100K and .02 cap to the B+ that's unused when stock. Each tube could have a 1640 resistor and a 25 cap that could be jumped to equal 820/50uF. All he'd have to do is move two wires and remove the jumper. The hi jack would be like adding a gain stage on ten. Is that too much gain?
I guess he could rewire the low jack with a pot, but I want to make him the stock amp he wants, and have a simple mod he can do himself without having to buy any parts, just moving a couple of wires around. I think he'd like that.

Second thought I'll use a pot. I'll send him the amp for Christmas, then on his birthday in Feburary I'll send him a pot, instructions, and a new faceplate so he can have a new amp he built himself for his birthday.

(It's late, I gotta go to bed, I'm ramblin')

[Shrapnel]

Jeff - there's an entire forum dedicated to the 18 Watt:
http://www.18watt.com/index.php
Of course, it's down right now.  Also, I didn't find it to be the friendliest place on the web but others must.

I've been on there before, as long as the amp sticks to some 1974 model topology you'll probably be OK. Try a Master Volume preamp with a split-load PI into EL84's and find your discussion shut down. At least some part of it HAS to match the original. (PA section WITH PI, or Preamp)

I wonder if it's tech problems with the site, or if there's something else. (I haven't been on there in a long time.)

[stingray_65]

Jeff!

What you are describing is a very common mod for the 18W.

Check out Doug's version he calls the Stout. http://www.el34world.com/schematics.htm
it's under the mods and projects

I'm going to be building it soon myself (no hot switch)

Very well documented, tried and true design.

He also sells the board and parts.

[Fresh_Start]

Jeff - Doah!  I was just too tired to post last night.  Doug's 18 Watt Stout is exactly what you asked about:


Bill - I adopted the pseudonym of "TheTinMan" for other forums after getting torched and then nuked simply for asking on 18Watt.com whether or not shielding heater wires might be an easier alternative to DC heaters.  I got detailed instructions on how to make and wear a tinfoil hat from several members.  Apparently anything Kevin O'Connor suggests is, by definition, heresy for those folks.

Doug Hoffman - Thank YOU!  This is the friendliest and most helpful tube amp forum I've found by a long shot.

Cheers,

Chip

[stingray_65]

Doug Hoffman - Thank YOU!  This is the friendliest and most helpful tube amp forum I've found by a long shot.

+1 !

I have to add it's by far the friendliest forum despite the topic!!

I kind of think it's funny when a Newb to this forum gets a short reply like "This has been discussed ad nauseum, see post yadda yadda" or a simple "yes or no" and they think they are getting a brush off or replied to condescendingly.

I haven't been afraid to ask the simplest questions in a long time here.

LOL that said, I think I'll post a question about voltage dividers 

Ray

[EL34]

Jeff,
Did you look at all the 18 watt info in the Library?

No need to re-invent the wheel over and over again.

[Ritchie200]

Stingray:  Yes

Fresh Start:

[Ritchie200]

 

[jojokeo]

Doug, was there any reason for using a .02uF c-cap leaving V1B before the 470k and then lowering the c-cap to .01uF before the pi rather than just using two .01uF c-caps instead?

[EL34]

Doug, was there any reason for using a .02uF c-cap leaving V1B before the 470k and then lowering the c-cap to .01uF before the pi rather than just using two .01uF c-caps instead?

I don't know
That was a long time ago and I don't remember why I did that.
Use 2 x .01's or 2 x .022's

The amp sounded good so I probably never messed with the original design