Can you please suggest a schematics?

[MCK]

Hi there. First off, please allow me to brand myself as a paint by numbers phase amp builder and move on to my question...

A while back I bought a Stancor 3801 with the intention of building an Express based amp one day. This OT happened to come attached to a home-built amp of some sort. Its an interesting build which looks like the old PA designs and has some strange (for me at least) pre-tubes like 6J7 and 6SK7. 6SL7 in PI and 5U4 for rectifier. Finally 2 x 6L6GB for power. As it is it works actually. You can see some photos attached to this post.

It has a Stancor 8412 as a PT which is not going to work for my eventual Express build and the chassis is good. While waiting to build my Express I decided to play around with this thing.

My plan is to rework it to get rid of the two prong chord first off and get 2 x 6SN7 in those pre positions and then rework the pre stage to be a little more guitar friendly. More than likely I will need to change the filter caps.

So the big question of the day... Can you think of an amp that has a similar tube setup to what I have in mind that I can rework this thing into? Any ideas will be most appreciated. Thank you very much!

[Phil_S]

With all respect for your desire to do this, paint by numbers often works poorly, particularly when you will need to do some improvisation with both design and layout to get a guitar amp circuit in there. The issues are numerous and I'm not inclined to be the one who starts to make a list.

I will say, however, you are showing a very nice platform. If this were mine and i wanted a relatively straight forward project, I might look at 3x 6SL7GT and keep the 6L6GB power section. The 6SL7 is a lot like a 12AX7, but a little less gain available. New ones tend to have heater related hum problems, but old USA made tubes can still be bought for fairly reasonable prices and I think they work much better.

There are lots of amps out there that use 3x 12AX7 and 2x 6L6. I think you will probably have the best luck looking at old Fender Marshall circuits. Don't discount the ones that have a pair of 6V6's as the preamp section is what you are really looking at.

This will be a lot to take on for someone without some experience. Think long and hard about what you are doing. I think, if you spend many hours planning, you may be able to pull this off. I think this is a place where the 80-20 rule will apply: 80% planning, 20% building. If you allow 20 hours building time, you have 80 hours planing time, and that is about right. That will allow you to learn a few things so you are not painting by numbers.

Because you have such an extraordinary platform, I think, if you can muster the patience, you wlll be rewarded with an extraordinary guitar amp.

[MCK]

Hi Phil, thanks for your kind input. Very well said. I was simply trying to announce my lack of in depth understanding at this stage when I branded myself as such.

I have built few projects before so I can safely execute to plans and get results but I am not at a point where I can say let me start from scratch and build etc. So that's why I was asking to see what I can build around this platform.

Agreed I will keep 6L6GB power section and change all pre tubes to 6SL7 so I don't need to change sockets. I just want to build something to learn more and prepare me for the next big project which will be the Express.

Problem is that eventually the 3801 will have to come out of this chassis so I don't want to get too attached. I will probably rework it yet again at that stage with another OT. Till then let me go schematics hunting...

[M Fowler]

You don't have to build this amp but it is a good example of using a choke to replace the field coil speaker in the old Gibson EH150 and the amp is a good blues or jazz amp.

Uses 6SQ7 preamp tubes, 6N7 PI and pair of 6L6's.

[MCK]

Thanks for that. Lets call it option 1. I came across Ampeg B15N as an amp with 3x 6SL7, 2x6L6GB & 1 x 5AR4. Trying to find schematics for it to see if I have most of the parts needed.

[Phil_S]

I think you'll find it here:
http://www.webphix.com/schematic%20heav ... ampeg.html

[MCK]

Thanks! Your help is most appreciated.

I think this particular one seems like a good fit : http://www.webphix.com/schematic%20heav ... taflex.pdf

Although the V2 is used for a second channel rather than a cascade stage. Can anyone think of another amp that is a reasonably good fit? Going once... going twice...

[ampgeek]

Consider the venerable Fender 5F6A (59 Bassman) for a 3X6SL7 pre-amp + 6L6 or 5881 PA. I have built a number of these over the last few years with nothing but praise from their owners. It still remains as my main gigging amp.

Follow the original schematic (changing only the 6SL7 pin out wiring) and tweak to taste. I typically split V1 cathodes and jumper V1 at the grids so that each volume control (normal and bright) can be used to dial in your desired flavor easily.

I have used both 6SL7 NOS and current production lately without hum problems. But...for a little extra coin....the 5691s are truly a treat to my ears!

Good luck!
Dave O.

[MCK]

Dave, sounds bassman sounds like a great idea. I've been hearing how many other amps are spinoffs from this circuit so learning this one might be a good place to start. Thanks for your suggestion. What PT & OT do you typically use in your builds? Regards

[ampgeek]

It is a really nice sounding circuit for sure! Pretty forgiving build due to its relatively low gain arrangement. It was the very first amp that I built ~5 yrs ago so it served as an excellent training ground for me.

The one that I just finished up used all Hammonds from Antique Electronic Supply (AES). Here are the AES numbers:

PT: P-T273BX (350-0-350)
Choke: P-CF22699
OT: P-T1650N (60W, 4,8,16 ohm + 70V)

My only "complaint" is that the OT needs Hammond's funky rotary switch to allow easy, on-the-fly impedance matching to various speaker loads. Works great...but a bit of a PITA to wire up. It's not needed if you will only be using the amp with one speaker/cab arrangement.

The young man that I built it for is a pedal steel player and he wanted a VERY high headroom, glassy clean amp and this build really delivered for him. I also threw in a one tube reverb circuit that worked out really well. he mated it with a 15" Weber Neomag in a 1X15" closed back cab.

I play in a classic rock cover band that covers LOTS of tonal ground so I need numerous pedals (most of which I build from kits) to get things "right". The 5F6A plan with octals takes every one that I have thrown at it like a middle aged house wife would take George Clooney's phone number!!

Cheers,
Dave O.

[M Fowler]

You could consider this Bassman as well the 5B6 here is a link to my build.

https://tubeamparchive.com/viewtopic.ph ... hlight=5b6

Mark

[MCK]

Thanks Mark. I will go this way since I want to keep this PTP. I might hit you with some questions if you don't mind. Appreciate your help

[M Fowler]

No problem let me know MCK.

I have the layouts and complete build instruction on this.

Mark

[MCK]

Thanks much! Most appreciated.

[passfan]

You don't have to build this amp but it is a good example of using a choke to replace the field coil speaker in the old Gibson EH150 and the amp is a good blues or jazz amp.

Uses 6SQ7 preamp tubes, 6N7 PI and pair of 6L6's.

Thanks for the scam. I have a bunch of these tubes laying around doing nothing.