New MarWatt Build with Modifications

[gktamps]

Updating this thread - finally got around to this one. Update post and photos in the most recent post...


On to the next one...

Though I have enough 18 watt Marshall variants now, I've got one more chassis I picked up cheap, along with these two transformers; a Radio Spares type from Heyboer, 290VAC, and a Partridge style low wattage OT with an 8k primary.

Decided to switch from EL84s in this chassis to 6V6s, and have come up with circuit board template with alignment marks to tubes and pots, but have made no decision about actual circuit or whether tube or SS rectified.

Sooo, anyone want to make some suggestions? Almost a blank canvas here, and I welcome your ideas.

Thanks!

Greg

[EtherealWidow]

*edit* Unfamiliar with Partridge OT's. They're PP? Maybe a simplified 6G3 would be cool.

[Smokebreak]

Marwatt?
http://mhuss.com/18watt/schematics/MarW ... sion21.gif
You could adapt for 6V6 and your PT seems well suited.

[gktamps]

EtherealWindow: yes, it's a PP OT.

Smokebreak: Hey, I forgot about the MarWatt - thank you.

[Lindz]

Trinity amps has a low watt Hiwatt (ha ha)

http://trinityamps.com/phpbb/download/f ... &mode=view

[gktamps]

Thanks, Lindz. Not a member of that board so will have to sign up before seeing that schematic.

[EtherealWidow]

Not sure if it's similar to the previously mentioned one, but here's another LoWatt from AX84.

http://ax84.com/index.php/oldprojects.h ... _id=lowatt

[M Fowler]

Thanks, Lindz. Not a member of that board so will have to sign up before seeing that schematic.

Here it is

[gktamps]

Thank you, Mark. That's an interesting approach. I will have to see what I can do to adapt the layout to this chassis. There is room for another preamp tube close to the end, and I could flip flop the layout.

[Smokebreak]

I built a single input version of the Trinity Triwatt/CP103(Townshend amp) . You could ditch the extra tube that way. Kinda mashed them together and approximated how Townsend had the unused channels set. Really great bell-like cleans, and aggressive breakup.
Here's the CP103 pre : http://hiwatt.org/Schematics/CP103PreRI.pdf

[gktamps]

I ended up going with the MarWatt design as a starting point. Since I have enough amps running EL84 tubes, this was built for 6V6 tubes. The PT is a standard 18Watt Marshall standup type by Heyboer, but I removed one end bell and fitted a laydown end bell and longer mounting bolts, since the laydown style chassis and transformers were inexpensive purchases I had on hand. The OT is a HiWatt DR504 style winding by Heyboer, and uses the original wiring colors.

Went with solid state rectification instead of tube, fixed bias instead of cathode biased. I like using 10-turn bias pots, so added one on the back panel, but didn't bother with test points, because I use a Compu-Bias. I dislike opening the amp to measure plate voltage in order to complete the calculations - can't figure out why test points are added for bias when the relative plate voltage changes, and may not even be known (or remembered or recorded in my case ).

Those changes necessitated modifications to the power side of the board, but I kept the rest of the circuit and board as drawn by Swanson. At least until I fire it up and give it time to see how I like the tone...

Since there was room, I added a CT fuse. I also ditched the ground bus bar in favor of the distributed grounds I've been using in all of my builds for some time now; not sure how it will work, but will find out later today. Have to get some chassis plugs for the empty tube socket holes.

One thing that puzzles me is why there is so little filtering for the preamp section, or at least, why there is only filtering at B+3 to also handle B+4 and B+5. I'll give it a listen, but was thinking I might want to add small filters at nodes B+4 and B+5 - can anyone please comment? In fact, please let me know if you have any other suggestions for how to improve this build.

Cheers,

Greg

[gktamps]

Pics...