5F10 Harvard Clone Project

http://i1016.photobucket.com/albums/af283/haircuttingcowboy/DSC00813.jpg
I made this turret board for my version of the venerable 5F10 Harvard. It's going into one of Boot Hill Amps 5E3 Chassis. If anyone needs one of these or any other turret board, PM me. I'll do what I can.

http://i1016.photobucket.com/albums/af283/haircuttingcowboy/DSC00812.jpg
The Harvard is a lot like a single channel 5E3 with fixed bias and NFB (Negative Feedback).

Some (especially those who build and sell such 5F10 clones) have made extravagant claims about the awesome tonal qualities imparted by the single 6AT6 and the (relatively newer) 6AV6 preamp tube.

They say the Harvard is the only amp in the old F lineup that utilizes it.

It seems useful for it's purpose in a single channel amp.

I bought a bunch of Soviet 7 pin tube sockets with shields. They fit the larger 12AX7 size hole with some hole reaming (on the socket only) and little coaxing.

So I can make some kits for youse guys.

Good on yah Dave, I knew you'd rise to the challange....but is there an off the shelf PT available? Mercury have a multi tap one for $145.....yike!

I've been using this one for 5E3 because it is well built - heavy with lots of plates - and (particularly) for 5E3 Proluxe 35 watt (pair of 6L6 power tubes) b/c it includes a 50V bias tap.

I shall use it for this Harvard Project. I know it works well for the lower output 6V6 pair in the 5E3. (I tape off the bias tap in this case.)

While the 5E3 Proluxe requires a massive output transformer, this Harvard will use the same one as employed in the standard 5E3.

Should work out well. Like I said, the Harvard is essentially a single channel 5E3 with fixed bias. (This is a great concept, IMHO.)

http://www.tubesandmore.com/products/P-TF41316

Yay. Cool. Excited to hear your thoughts compared to 5e3. I don't even think I've seen a Harvard. *google* do they have more clean headroom?

I suspect compared with the 5E3 that they do stay cleaner longer before breakup. Fixed bias and NFB contribute to that.

This particular amp will be dimed on stage for the later break up distortion - awesome tone derived from driving a small amp hard. Mic'ed through the PA also.

Should do well for that.

Cool find, but it's only a 120V tap. I'd have to use a step up trans which I've done before anyway.

http://www.tubesandmore.com/products/P-T290BEX

For our Friends in Europe and Down Under, Here's a 240V Hammond that will fit. More expensive, of course.

Good on yah Dave, I knew you'd rise to the challange....but is there an off the shelf PT available? Mercury have a multi tap one for $145.....yike!

My take has always been build it on a 5F2 chassis and use a Champ PT. Punch an extra 5/8" hole and you're good to go.

Allen's TP25 has a bias tap and all the current you'd ever need.

...except Allen doesn't do export so it's not available with a 240v primary.

...which might be a good reason to build it on a 5E3 chassis. Bigger transformer knockout and plenty of 240v choices.

I can't see why it needs three inputs, either. Two works fine for me.

On my first one, I used only two inputs, but on my current project I am using three. In reality, only one is all that will ever be used, but...

I hope you all realize with this kind of talk it will be real hard for me to not to start building one myself when I get my 12AT6's in the mail.

We're like cats on heat :lol:

This place is starting to feel like it's grabbing a hold of me like a street drug. Just this morning I was thinking how I need to starting weening myself off this site, now Hackworth comes in with a Harvard build thread! I love it! Another week of entertainment watching this unfold. Please keep up the great work with the photos Dave.

The 6AT6 tube caught my attention. I have an old RCA 12AV6. Is this like a 6AT6, but higher gain factor and 12V heater wires?

The 6AT6 tube caught my attention. I have an old RCA 12AV6. Is this like a 6AT6, but higher gain factor and 12V heater wires?

Seems that's the deal

One half of a 12AX7. There has to be something useful to do with those diodes. Wonder if anyone ever made a clipper circuit with them?

On my first one, I used only two inputs, but on my current project I am using three. In reality, only one is all that will ever be used, but...

Where did you find that 5F10 chassis?

Just a few thoughts,

Seems like that PT would really be a lot of overkill in a 5F10 which ran the plates at 305V +/-
A good part of the tone & breakup came from the lower operating points throughout the circuit.

Yes, you are right, EdMax. Although In this case, more power is desirable. Not going for a purist build, but your point is valid, for sure.

I anticipate preamp voltages to be about par with a 4.7K ohm dropping resistor as seen in the 5E3.

It appears that the original Harvard with its smaller PT, used a 470 ohm resistor for the power tubes screen grids.

The Richter 'Charm School' is the only clone I could find with a three input chassis.

Victoria has the triple inputs on a conventional Fender Style chassis.
http://www.victoriaamplifier.com/wp-content/gallery/ivy-league/dsc_0596.jpg

Where did you find that 5F10 chassis?

On the first one the chassis came from Mojo. It isn't a Harvard chassis but one that some one asked Mojo to make several of and the tube configuration and pot configurations were what I needed for the project.

On the second one, and the one I suspect you are asking about, I thought, who makes a Harvard clone? I called Victoria Amps and spoke to the guy that owns the company about buying one of his chassis. I told him what I had paid for other chassis. He thought about it for a moment, looked up his costs, and asked where I wanted it shipped.

http://i1016.photobucket.com/albums/af283/haircuttingcowboy/Harvard022.jpg
Populated Board

Wots the specs of the bias pot Dave?

http://i1016.photobucket.com/albums/af283/haircuttingcowboy/Harvard016.jpg
These hands-free devices help to hold the board so you can solder along the turrets.

http://i1016.photobucket.com/albums/af283/haircuttingcowboy/Harvard018.jpg
Cut and wrap component leads so they make 3/4 of a turn around the turret. Do what you like. 3/4 is Mil Spec. Enough for solid contact and not so much that it is difficult to desolder and remove for future service replacement.

http://i1016.photobucket.com/albums/af283/haircuttingcowboy/Harvard023.jpg
Just two inputs into one channel. The pure Harvard has three inputs.

http://i1016.photobucket.com/albums/af283/haircuttingcowboy/Harvard025.jpg

http://i1016.photobucket.com/albums/af283/haircuttingcowboy/Harvard029.jpg
Typical wire lead length is 3.5 inches. Choice of colors is de rigueur.
Wires are soldered into the holes in the tops of the turrets.

http://i1016.photobucket.com/albums/af283/haircuttingcowboy/Harvard031.jpg
Back of board. I forgot the lead for NFB.

Wots the specs of the bias pot Dave?

2W 1k resistor on the front, 25K pot with a 27K 1W resistor as fail-safe. Two 10uF 160V caps.

So in the orig schematic, there is no bias pot...just a 6.8k, a diode, a 56k and a 25uf cap. Your making it more versatile?

So in the orig schematic, there is no bias pot...just a 6.8k, a diode, a 56k and a 25uf cap. Your making it more versatile?

Adjustable and failsafe. That way you can tweak the bias into a tube set's sweet spot.

Here's some good info on bias circuits. IIRC, tubeswell put this up the other day:

http://www.el34world.com/charts/Biascircuits.htm

http://i1016.photobucket.com/albums/af283/haircuttingcowboy/Harvard5f1006.jpg
http://i1016.photobucket.com/albums/af283/haircuttingcowboy/Harvard5f1003.jpg
http://i1016.photobucket.com/albums/af283/haircuttingcowboy/Harvard5f1004.jpg
http://i1016.photobucket.com/albums/af283/haircuttingcowboy/Harvard5f1005.jpg

http://i1016.photobucket.com/albums/af283/haircuttingcowboy/harvard15001.jpg
Beautiful Simplicity of the 6AT6 tube socket. Did I do it right?
http://i1016.photobucket.com/albums/af283/haircuttingcowboy/harvard15002.jpg
V2 gets a 12AX7

http://i1016.photobucket.com/albums/af283/haircuttingcowboy/harvard15003.jpg
Pair of 6V6 power tubes go here.

http://i1016.photobucket.com/albums/af283/haircuttingcowboy/harvard15004.jpg

http://i1016.photobucket.com/albums/af283/haircuttingcowboy/harvard15005.jpg

http://i1016.photobucket.com/albums/af283/haircuttingcowboy/harvard15006.jpg

This amp is a screamer. Really delivers. I tested it for an hour hard with a strat and a Weber Legacy 12 inch 50 oz magnet, British style, 65 watt speaker in a combo cab. Nice speaker, IMHO.

Transformers stayed cool. Lots of treble and plenty of bass. Less midrangey sound than the 5E3. More bite. Less sustain, Less blossoming. Less finger sensitivity. More direct kick in the pants.

I installed an 250K intensity pot (adjusts bias) rather than the NFB pot. You can really dial in some great sounds.

I am a fan of the Customized (5e3 Transformers) Harvard.

I got mine wired and operational this past week. Hooked it up to a 2 - 12 cabinet and tried it out. Break-up starts about 5. No complaints about the tone. Next step is to build a head-only cabinet.

This amp is a screamer. Really delivers. I tested it for an hour hard with a strat and a Weber Legacy 12 inch 50 oz magnet, British style, 65 watt speaker in a combo cab. Nice speaker, IMHO.

Transformers stayed cool. Lots of treble and plenty of bass. Less midrangey sound than the 5E3. More bite. Less sustain, Less blossoming. Less finger sensitivity. More direct kick in the pants.

I installed an 250K intensity pot (adjusts bias) rather than the NFB pot. You can really dial in some great sounds.

I am a fan of the Customized (5e3 Transformers) Harvard.

It'll be interesting to hear it with an Alnico, I think the origs had that set up.

I will get the parts together for a kit and post it in the vendor section here.

You can build it with Cathode Bias or Fixed adjustable bias.

With Cathode Bias, it will be much like a minimalist, single channel 5E3. The difference is the 6AT6 or 6AV6 triode which imparts its unique tonal signature.

For some, a 5F10 kit will provide an easier build than a 5F1. The 5E3 chassis offers more interior space in which to work. Two input jacks up top going into one channel offer no interference whatsoever with the board below.

Plastic plugs will be included in order to plug the unused holes.

Harvard 5F10 offers a step-up from the SE 5F1 Champ Build, with less detail than the 5E3. Fewer parts means fewer things to go wrong.

Surely, the 5F10 type stands as the simplest of Push-Pull Tube Amplifier Design (which is a cool thing in itself).
____________

More about this version I built:

Projection. This amp "projects" its sound. The sensation is such that it makes one feel that it will be heard in the back of the bar room. It has a particular "bark" to it. I mean that in a good way. Very Cool sound.

guitar1amp2000,

What transformers have you in yours?

Cool HWorth. I have a friend who needs a simple amp like this. I didn't read the whole thread, but does it have a little more clean headroom than the 5e3? Thanks!

Cool HWorth. I have a friend who needs a simple amp like this. I didn't read the whole thread, but does it have a little more clean headroom than the 5e3? Thanks!

Yeppers. I am very impressed with it.

So... Are you going to offer a kit??

http://i1016.photobucket.com/albums/af283/haircuttingcowboy/Harvarddone008.jpg

Here is the Harvard 5F10 in a 5E3 Chassis in a 5E3 Combo Cab. Two jack holes are plugged. Two knobs are mislabeled. From right to left they are volume, tone and the little knob on a 250K pot is "intensity". Great knob that adjusts the bias from mild to wild with no redplating, of course.

Nicely done...have noted for a future build. Could you have the bias in the middle, then the tone knob would tie in with the tone position?

I would really love to hear a sounds clip of this with the adjustable bias. I am very interested to hear the sweep from mild to wild.
Dave, are you considering placing an order for custom chassis from your supplier? With 2 inputs, and proper knob labels for this? I am certainly interested in building this kit, especially if it had the proper chassis.

Nicely done...have noted for a future build. Could you have the bias in the middle, then the tone knob would tie in with the tone position?

Sure.

I would really love to hear a sounds clip of this with the adjustable bias. I am very interested to hear the sweep from mild to wild.
Dave, are you considering placing an order for custom chassis from your supplier? With 2 inputs, and proper knob labels for this? I am certainly interested in building this kit, especially if it had the proper chassis.

You would love this amp. I've listened to your playing (which is quite good). Take me a while to get clips. Chassis-wise, that's a good question.

As a repeat customer, take one like this (chassis kit with 5E3 chassis) for $150 plus $20 shipping to CA.

I only have a few 5E3 chassis on hand right now (and zero Harvards).

My goal was to prototype a simplified - trimmed down 5E3 build. The fixed bias adds a level of complication, but the other end is significantly simplified and pared down to the barest essentials.

The fixed bias and that intensity control (which I stumbled upon as a way to fill that extra hole) is what makes this amp different (punchier, crisper) than a 5E3 (which is a wonderful amp in its own right as you are well aware).

Since I built my 5F2A, my 5E3 is mostly collecting dust as 90% of my playing is at home. The 5E3 is indeed a great amp. It's a bit of a bully to dial in tone wise without annoying my family and damaging my own hearing. The 5F2A solved most of that for me. Where does your modified Harvard fit in between those two?
Being 2 6V6's is it as loud as the 5E3? I am not really looking for more clean headroom. At home the 5F2A is clean enough. Your intensity control sounds really interesting. Does it shape the OD gain? Or more so the color of the tone? Or..? For reference, the NFB pretty much stays off on my 5F2A as I like the crispy bite it provides. Your comments are appreciated.

Project completed.