50 Watt to 100 Watt Conversion

[kd]

Question for those that have played, own or have owned both a 50 watt and a 100 watt non HRM amp. I keep reading that the 100 watt sounds "bigger" and has more "girth" to it. I built a 50 watt ODS 101 non-hrm about a year ago. I'm thinking now of rebuilding it to 100 watt specs using a Marshall 100 watt PT so I can run EL34 tubes if I choose to. For the OT I'm looking at the Marshall 100 watt OT from Magnetic Components.

What do you guys think, good move or bad?

One more question, does the 100 watt use a Fender Twin Reverb choke?


Thanks,
Ken

[David Root]

Easy one. If you build a complete new 100W amp (with that excellent MC Marshall 100W OT), you can compare them and make your own decision!

Seriously though, that is the cleanest way. Modifying a 50W chassis for two more octal sockets, all new new iron, yes you will need a twin choke, but it's a lot of work. I have done it recently, turning a bassman chassis into a four holer. (Four 6L6GAs, so not 100W, but still the two pairs, which is what does it).

If you do modify the 50W, don't forget that pin #1 is connected in the EL34, so if you were using 6L6GCs and used pin 1 to bridge the screen resistor to pin 4 you will have to relocate that end of the resistor somewhere else, otherwise you'll have screen voltage where it shouldn't be and no screen supply.

[kd]

Thanks for the reply David. I have too many amps now, so I'll only allow myself to have one Dumble type amp which means upgrading the 50 watt amp. There are spots were I'll have to be careful but the chassis is large so it won't be as bad as it seems.

If you do modify the 50W, don't forget that pin #1 is connected in the EL34, so if you were using 6L6GCs and used pin 1 to bridge the screen resistor to pin 4 you will have to relocate that end of the resistor somewhere else, otherwise you'll have screen voltage where it shouldn't be and no screen supply.

Good advice, thanks.

Ken

[M Fowler]

Keep or sell the 50w and get the correct chassis to build your 100w. $0.02

[johan]

Seriously though, that is the cleanest way. Modifying a 50W chassis for two more octal sockets, all new new iron, yes you will need a twin choke, but it's a lot of work.

New choke? Isn't the choke the same in Twin vs Bassman amps? 50 vs 100W amps?

[kd]

New choke? Isn't the choke the same in Twin vs Bassman amps? 50 vs 100W amps?

AFAIK they are the same, but my amp doesn't currently have a choke. I'm using a resistor in its place.

Ken

[John_P_WI]

Check out London Power's kit:

http://www.londonpower.com/catalog/prod ... ucts_id=74

If you have the room, it is a simple solution and the technology works well. Yes, there is a difference in feeling too, the amps feel faster and lest congested.

John

[wicker]

Use higher voltages (new PT) and change 6L6 to KT88 ?

[Structo]

What chassis did you build your 50w in?

[kd]

Hello guys,

Use higher voltages (new PT) and change 6L6 to KT88 ?

What is the benefit of the KT88 over the 6L6 tubes?

What chassis did you build your 50w in?

I bought a 20"x 8"x 2.5" blank chassis from Watts audio. It's plenty big for this purpose.

Ken

[talbany]

Use higher voltages (new PT) and change 6L6 to KT88 ?

KT-88's can dissipate upwards of 40w each at around 500v.. If you go with the 88's in place of the 6L's do the math on the output transformer as well.. a 50w OPT wouldn't last very long with a pair of those puppy's pushed!!
Thought I'd mention

Tony

[tubedogsmith]

Here's an oversea's 50 watt chassis I just converted to 100 watt. Clean master added on the front, FET gain and presence knobs added to the back. It came out great.

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[kd]

Thanks Tony, I don't know a thing about KT88 tubes.

Ken

[Structo]

http://www.mif.pg.gda.pl/homepages/fran ... k/KT88.pdf

If you haven't got it, I recommend that you download the Duncan Tube Data Sheet Locator.

It's an invaluable tool for vacuum tubes.

http://tdsl.duncanamps.com/

[kd]

Thanks Tom. I have it installed on my computer. I generally don't stray too far from the old standards, so I've never heard a KT88 tube.


Ken