Harvard 5f10 build

[jewishjay]

ok....I'm in the pre planning stage of a Harvard 5f10. Here's what I've got so far:

a vintage Thordarson (380vct with 5v and two different 6.3v)
a new Hammond 1750E (15w 8.5k  8ohm)
a 12" Jenson
a pair of Electro Harmonix 6v6 and a Sovtek 5y3

since my PT doesnt have a bias tap, I'm planning to derive it the Marshall way from on leg of the HT. I also want "bass" and "treble" instead of just "tone"

I would appreciate your experienced eyes on this schematic before I start punching holes in a eyelet board. does this look ok?

[sluckey]

So, you want a Princeton sans tremolo...

     https://el34world.com/charts/Schematics/files/Fender/Fender_princeton_aa964.pdf

[jewishjay]

So, you want a Princeton sans tremolo

I suppose thats another way to look at it, although the 6at6 vs 7025 has to count for something, and the way i've drawn the bias circuit is lifted from robrob and much more adjustable..

[ac427v]

I built a variant of the cj11 that can do clean, tweed and rock out. Don't tell anyone but it is the favorite of my creations.

[jewishjay]

I built a variant of the cj11...

thats really different.  what are those two 250k pots between the phase inverter and power tubes?

[ac427v]

That is a dual pot for the Lar Mar Master Volume. Two pots that share one shaft. When you turn the knob, both pots move the same amount and affect the amount of signal going from the phase inverter to each power tube. I tried that MV and a different MV using a dual 1M audio pot. I prefer the latter but the Lar Mar gets all the internet glory.

[bmccowan]

6at6 vs 7025 has to count for something

I think it does - one less gain stage, right? But I think the biggest difference between the 5f10 and the 964 is the much lower B+ voltage in the Harvard. Can you get down in Harvard range with that transformer?

[jewishjay]

Can you get down in Harvard range with that transformer?

oh...maybe not. do i understand this correctly? 375-0-375 into a 5Y3 = ~ 412 ?

if that's right, its much too high, there's no good way to bring that down to 315 320 ish.... i need a different transformer....or different power tubes....

[sluckey]

I have a real 1957 5F10. Here's my voltages...

     http://sluckeyamps.com/harvard/harvard_5f10_schem.pdf

[bmccowan]

I guess I shouldn't be surprised - much higher than the "official" Fender schematic shows. I have a real one too. Of course, I have no idea where voltages I recorded might be, but now I'm curious and will check. Sweet little amps.

[sluckey]

Mine has a replacement PT from David Allen. I suspect my voltages are a bit higher than the original PT, but it's still a nice amp. Since it's fixed bias B+ can run higher.

[jewishjay]

I have no idea where voltages I recorded might be, but now I'm curious and will check. Sweet little amps.

I would appreciate that, especially if yours has the original PT

[bmccowan]

Jay,
Easy amps to get to the circuit, so I opened it up at lunchtime. Yes mine has the original PT. With an AC wall voltage of 118, my B+ voltages are 366; 362; 291. So, higher than the Fender schematic shows, but lower than those in Steve's amp. I'm sure the Harvard sounds great at 400+ volts. I find my Harvard sounds more mellow/jazzy/browner like the early Gibson and Valco amps that also have lower B+ voltages than BF/SF Fenders. I may attribute too much to the voltage thing  but it seems Fender kept raising the voltage to get the amps louder/cleaner/punchier.
Steve I note that you kept the selenium diode, as did I. But I keep reading that its at risk of dying and taking hostages with it. What do you think?

[jewishjay]

Thanks so much. Now, the 6V6 datasheet lists 315v as MAX plate voltage, so I was thinking if my B+ is over 400v to use this pair of Russian no name 6L6GC instead. But with the voltages you two have measured, maybe I'll stick with the Electro Harmonix 6V6GT I originally planned?

[DummyLoad]

Thanks so much. Now, the 6V6 datasheet lists 315v as MAX plate voltage, so I was thinking if my B+ is over 400v to use this pair of Russian no name 6L6GC instead. But with the voltages you two have measured, maybe I'll stick with the Electro Harmonix 6V6GT I originally planned?

fender pushed 6V6 to over 400V+ on several amps. no need to worry about NOS tubes running 400V+ if biased as fender did. IIRC the AB763 deluxe was designed to run with 420V B+ to OT CT.


--pete

[jewishjay]

cool, so I will move forward with what I had planned for this "high voltage" Harvard and save the 6L6s for a future Bandmaster 5E7 project.

I can post a picture of the eyelet board soon....

[bmccowan]

Or you could save that PT for the Bandmaster project and get a lesser PT for the Harvard. I have recently bought some nice lower voltage PTs from Musical Power Supplies https://www.musicalpowersupplies.com/products/ - aka Musical Matt on ebay. With Classic Tone going out, I hope Matt sticks around and expands his offerings.

[jewishjay]

Or you could save that PT for the Bandmaster project and get a lesser PT for the Harvard. I have recently bought some nice lower voltage PTs from Musical Matt

thanks. I have another similar PT for that project already. but looking over Matts offerings i see that some of the lower voltage PTs are rated only 100 mA. would that be enough for (1)6at6 (1)12ax7 and (2) 6v6 ?

[jewishjay]

Here's the populated eyelet board, and my thoughts on the layout so far.

[bmccowan]

Yes 100ma is enough. But some of his other lower voltage PTs have higher amperage ratings. Weber's PTs often have two B+ taps, but I try to avoid Chinese products these days. Not because they don't make good stuff, but because they cheat US companies out of intellectual property.

[sluckey]

Steve I note that you kept the selenium diode, as did I. But I keep reading that its at risk of dying and taking hostages with it. What do you think?

I think it's cute. I ain't scared. Anyone that eats one that size or stands around smelling the rotten egg odor of a shorted one long enough to cause lung damage probably should be eliminated from the gene pool anyway.   

[bmccowan]

  Thanks Steve. The cute one survives!

[sluckey]

Once the world was a safe place to live. Then someone invented MSDS! Now there are a few nervous survivors. They spend a significant amount of time ensuring there MSDS are up to date and filed in the cabinet next to their safety board. It's dangerous out there. Y'all be careful now.

[bmccowan]

To that point I recently bought an aluminum step ladder. On the ladder is a sticker that cautions that it contains substances that are known to cause cancer in the state of California. I looked at my wife and said that luckily we will not be using this ladder in California.

[AmberB]

All of my old (1960s) model train transformers had selenium rectifiers in them...  :-)

[bmccowan]

OMG, I gave my 1960 Lionel to my Grandnephew - what have I done!? On the other hand, he doesn't live in California either.

[shooter]

Then someone invented MSDS!

 

[vampwizzard]

Here's the populated eyelet board, and my thoughts on the layout so far.

Looks good! solid stuff

[jewishjay]

Productive day yesterday. Built the cabinet, it's almost ready for tolex, and prepped the chassis.

[jewishjay]

Today I wrapped the cabinet in this rich chocolate brown leatherette with a brown leather handle and brown plastic feet.