Tweed Harvard/Bassman Build Thread

gabasa

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Here we go ... obviously it seems that I haven't built enough Bassman amps. I have a Victoria Ivy League chassis courtesy of our very own @David Barnett and am building a tweed Bassman circuit into it. I already have a Harvard build that I've enjoyed immensely and don't want to build another.

Here's the basic idea:

-Harvard chassis (3 inputs, 1 volume, 1 tone)
-Single-channel 5F6A Bassman circuit
-6AT6, 2x12AX7, 2x6V6, 5Y3
-330k resistor to replace bass pot
-12k resistor to replace mid pot
-2.7k resistor to replace presence pot
-fixed bias
-5E3-sized cabinet
-Perhaps a 12F150 or 12A150A

Basically, a wolf in sheep's clothing.
 
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gabasa

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Here's what I've done so far. I can't seem to find a 250pf cap in my box; I need to look again or purchase one:

Harvard-Bassman board.jpg
 

gabasa

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This is the PT that I'm considering:


It's 325V-0V-325V @138mA, which is a hair lower voltage than Hammond's 290BX. Why not.

I have a little Marvel choke from Antique Electronics supply that I've never used.

For the OT, it's a tossup between a 50246 wind or a 125A1A wind. I might go for the latter because my gut tells me the 6.6k is louder. However, I love the bottom end of a 50246. Not sure yet.
 

NTC

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If you use a 6.6k primary, you could use this amp with 6L6's as well. That PT will ne up to the job, albeit barely. You would have to use a 5U4 or 5AR4 rectifier tube. My 5F11 works this way. In my case, the two tube compliments I have bias at about 68% dissipation without changing the bias voltage.
 

NTC

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And from the Department of Bad Names, call it Harvey Bassman.

I can't help myself: another possibility is Harvey Bassmaster, given your past Traynor experience and location.
 

gabasa

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I can't help myself: another possibility is Harvey Bassmaster, given your past Traynor experience and location.
Lol, how about Harvey Master?

Since I have this chassis and wanted to do something unique, I went this route because it miminized my costs based on what I have in my junk boxes. For the eyelet board, I wasn't missing much for this amp so I picked up the little I needed from PartsConnexion.

I just ordered a few parts I need from CE Distribution and the the transformer order is also going in today. I was going to use an OT I have here but I'm going to splurge on a new one.
 

Mongo Park

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Oh man, love the baseman this should be one sweet build considering the variation you are planning.
Watching to see how it turns out.
Being famously loud you should be fine with 6V6 power tubes
 

gabasa

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Oh man, love the baseman this should be one sweet build considering the variation you are planning.
Watching to see how it turns out.
Being famously loud you should be fine with 6V6 power tubes
Thanks, I’ve been addicted to tweed Bassman variants ever since I discovered ‘60s Traynor Bass Master amps in the 1980s.

I figured that a 6V6 version with an efficient speaker might give me a good amount of volume in a portable package!
 

NTC

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Thanks, I’ve been addicted to tweed Bassman variants ever since I discovered ‘60s Traynor Bass Master amps in the 1980s.

This is my story as well. My first amp was a 69 era YBA-1. The first time I played through a Victoria Bassman clone, it had a VERY familiar sound.
 

gabasa

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My Harvey Bassman chassis is assembled, notice the new V3 I added. I know I have to remove the pilot light assembly to squeeze in the eyelet board; I just couldn't help assembling all the hardware! Everything is now on hold until I get my PT in the mail.

I ended up ordering a Brownface Deluxe PT from Pacific Audio Magnetics, which is 325-0-325 V @138mA.
For the OT, I'm going to use an SSTDR from Soursound, which is unique. It apparently combines elements of both the 50246 as well as the 125A1A output transformers. It's more modern sounding than the 50246, but not quite as "modern" as a '60s OT.

Pacific and Soursound in the same amp? Can I go wrong?

Harvey Bassman Chassis.jpg
 

gabasa

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Update! I received my Soursound OT today and bolted it to the chassis. My next step will be to fasten my eyelet board to the chassis and start hooking up the wires.

I ordered the SSTDR model. It's a cross between their 1839 and 125A1A. Apparently it's more interleaved than the 1839 but not as much as the 125A1A, and all-paper (no mylar). Bryan Sours describes it as more modern than the 1839, but not a decade more modern. I'm looking forward to hearing this OT.

Chassis with Transformers.jpg
 

gabasa

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Got my eyelet board installed now that my transformers are all in. All that's left are the hookups and final assembly into the cabinet.
Hmmm ..... for a 1-channel 6V6 Bassman circuit, would you put a 6AT6 into V1 or a 6AV6?

Board Installed.jpg
 

mountainhick

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Hmmm ..... for a 1-channel 6V6 Bassman circuit, would you put a 6AT6 into V1 or a 6AV6?
How much drive do you want? historically was 12ay7, so less gain than either single triode, but 2 channels could also be jumpered. Sounds like experimentation could be useful.
 

gabasa

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How much drive do you want? historically was 12ay7, so less gain than either single triode, but 2 channels could also be jumpered. Sounds like experimentation could be useful.
Because I have a Harvard build, I have a few dozen each of both types of tubes. I guess I'll experiment with both, then hunt for a quiet one.
 




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