1956 Fender Harvard

[rfgordon]

Just for hoots, here are some pics of a 56 Harvard that came in for service. The only thing wrong with it was a completely trashed speaker.

Through my early 70s Greenback, the thing kills! Even though original, the caps still have a strong reservoir. Great amp.

[martin manning]

Nice, Rich, thanks for posting. I've considered building a Harvard clone at some point. Did you by chance get a measurement of the line voltage and PT secondary VAC going into the rectifier? How about B+?

[Structo]

Is that a 5F10?

[morcey2]

Is that a 5F10?

Should be. The 6G10 is single-ended and only has 3 tubes. The 5F10 is PP and has 5 tubes total.

There was a 5F10 at one of our amp shows about 5 years ago and it sounded awesome. I have a couple of 12AT6 and a pair of 12V6 that I "commandeered" from some old organs and radios and I might build a 12-volt heater 5F10 from them.

Matt

[rp]

Of my clones this one turned out the best. Special little sucker. It your chart says 6AT6 try a 6AV6, the later charts spec'd it. It really takes off with the higher gain tube, not like a 5E3 which I actually prefer w/ the 12AY7 as it seems to loose trajectory with the 12AX7. Lucky owner, hopes he finds a proper speaker. Worth hunting down something from the era, ceramic is fine.

[martin manning]

Hi rp, I read your 5F10 thread with interest a while back. I was thinking I'd go with a noval socket for V1 and use a 12AX7, which is electrically equivalent to 6AV6. I could add a switch to use one side or the other, and, I wonder what it'd sound like with the twin triodes paralleled?

[ToneMerc]

Nice, Rich, thanks for posting. I've considered building a Harvard clone at some point. Did you by chance get a measurement of the line voltage and PT secondary VAC going into the rectifier? How about B+?

I would love to know was well, in addition to the AC at the bias tap. I'm thinking that bias tap is only 30-35 volts.

TM

[Colossal]

Been doing some reading on this amp. I found a post by Tubeswell elsewhere that suggested 280 to 285-0-285 to hit the published B+ of 305VDC with a 5Y3GT (a real one). Bias tap at 50VAC.

[ToneMerc]

Been doing some reading on this amp.

Dave, same here. There are several builds on the net and I have yet to run across one that had the correct target voltages with typical off the shelf iron. I haven't verified it, but even MM iron seems way off. I still don't see how this model had a 50V tap, 30 I can believe. seems to me, the 50V tap would plant bias voltage in the mid 40's range.

I spec'd this out earlier today; I'm leaning towards a 125V primary, 285mA @110mA, 3A @5V , 2A @ 6.3VCT and a 32V bias tap. I have a 15W Partridge style OT that should work well for this.

TM

[ToneMerc]

Found another bit of info that the original bias tap was 35V, so if that can be verified, it would clear this up for me.

TM

[martin manning]

This PT is a Champ/Princeton type, so I would say start with a Fender 022772 replacement. The 6.3V @2A and 5V @2A are fine as-is, but for the HT I think lower it to 540 CT (270-0-270) at the nominal 70-80mA, and add a 35V bias tap. Bias voltage on the Harvard schematic is -27V, and that looks good with a 35VAC input using the component values shown. Heyboer could just modify the HT on their HY022772 to meet this spec. You guys interested in doing a group buy to get a few of these? HY022913 Princeton OT would make a good match.

[jon]

I've built a few Vibrolux 5F11 amps over the years, and I can tell you that a tweed champ transformer settles into the voltages almost perfectly under load.

[martin manning]

5E11 and 5F11 have 35V higher B+ on their schematics relative to the Harvard. There is a Hammond replacement for Champ, Harvard, and Vibrolux Tweed, 290CAX. It has two sets of secondaries, 630 and 550 CT at 110mA, and no bias tap. I think the 550 CT will come out a bit high (20V ?) at the idle condition, but it is very close for off-the-shelf. Nice that they give loaded and no-load voltages on the spec sheet.

[Structo]

I would love to own all the models from 1956, the year I was hatched.

[Teleguy61]

Plug a Tele into that thing and start playing Cropper licks.