Where to learn about power sections?

[JamesO]

Hi everyone

This doesn't have anything to do with Dumble style amps, but I'm hoping to learn about power sections. Specifically how to change my cut my 15 (from two EL84's) watt Lightning down by half or so. Any ideas? I'm trying to make a bedroom level amp.

[Funkalicousgroove]

I'd read:

Dave Funk's Tube amp workbook

Valve Amplifiers by Morgan Jones

And I believe Kevin O'connor has an entire book on power scaling.

THere are a couple of ways you can cut the power/output level, the simplest way is to play through smaller/less speakers.

the second easiest would be to play through a power brake/Hot Plate, etc.

The third would be to install a power scaling device(I believe there is a schematic in the files section).

[benoit]

Little bit of a hijack, but funk, would you recommend those books for general tube amp info? I can read a schematic/layout in terms of what components are, what connects to what, etc, and know enough about saftey issues and soldering that I could get an amp together, but I'd like to really understand how the amp works so I can tweak intelligently.

[drz400]

Little bit of a hijack, but funk, would you recommend those books for general tube amp info? I can read a schematic/layout in terms of what components are, what connects to what, etc, and know enough about saftey issues and soldering that I could get an amp together, but I'd like to really understand how the amp works so I can tweak intelligently.

\
The London Power books are good for that but you kind of have to buy them all since he refers to previous chapters in other books

[JamesO]

I'll have to check those out. I read through the section in The Guitar Amp Handbook, but it doesn't really go into many specifics. The article on the Aiken Amplification page on push/pull vs. single ended gives me something to go on, but I'd like to know more about filtering and how you get those tubes to put out a target wattage. Two EL84's putting out 8 or 10 watts instead of 15, etc.

[ampgeek]

Hey James,
Can you direct us to a schematic of that amp? Some pictures would be helpful as well.

Power output is directly proportional to the tubes voltage drop (plate to cathode) and tube current flow. Reduce one/both, and output power will drop.

Of course, lots of other things change as well when moving away from the "optimum" voltage and current condition. Some may not be desireable in terms of tone.

One easy thing to consider is reducing the output tubes plate supplies.
Typically, that means mucking around with the B+ string/dropping resistors but it shouldn't be to tough to test it out.

How are the output tubes in this amp biased? That would be the first thing to look at for reducing current flow.

Dave O.

[JamesO]

Thanks dave!

The powertubes are cathode biased.

This is the schem and layout for the Lightning I started with (done by Stephen at Trinity). This is basically what I'm putting together, with a toggle to take the bypass cap on and off of V2, no master, and experimenting with some different coupling caps. This was my first amp, last summer.

Schematic: http://languagepool.net/amp/lightning/T ... ematic.jpg

Layout: http://languagepool.net/amp/lightning/T ... t_rev2.jpg

[ODwan]

Hi James,
I recomend KOC's books (all of them!) as well as Dave Funks book.
BTW 8-10 watt won't give you a bedroom level amp! Even 2 watt Mini Blues Express can be loud enough to wake my 2 years old son, if I crank it in the basement! Smaller and less efficient speakers is surely a good way to go. Look for old tube radio speakers. Most are 6" to 8" pretty good sounding and of low to mediocre efficancy.
Keep on rockin',
Timo

[ampgeek]

My pleasure James!

That looks like a sweet little amp.

Timo is absolutely correct. Even a couple of watts can create some clatter.

What type of music do you play and what type of tone do you look for? Also, what size/number of speakers do you have (if any).

These answers might help guide your decision on how to go forward.

If you are still assembling, I would seriously consider Funks suggestion of a power scaling system. You can check them out here (poke around a bit to find their scaling kits and boxes):

http://www.londonpower.com/

and you can hear what appears to be a pretty objective test at this site.

http://bruceclement.com/music/psk.htm

There is also a thread on this topic here at the ampgarage technical section.

https://tubeamparchive.com/viewtopic.php?t=1222


I haven't tried this technology as of yet so I can't speak from experience. But...I have heard others say it is pretty good.

Dave O.

[heisthl]

Here's an easy way to see if power scaling is for you - works pretty well and is super easy, it just changes the PI voltages
Exerpt from Carvin schemo attached:

[JamesO]

Thanks guys. I'm going to take some time to look over these things.

I'm off now for a vacation. See you in a week!

[llemtt]

James

just one more suggestion: power scaling is really cool (I actually don't build an amp without it) but don't expect bedroom levels without tone compromises, TUT4 from Kevin is the right starting point to the whole subject.

First item on the buy list should be a really inefficient speaker!! (quite the contrary to ordinary guitar speakers..)

cheers
Teo