HawkeyeKane
1873 posts
Jul 10, 2013
11:00 AM
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With the recent discussion of circuitry similarities and differences in the 74 Musicmaster thread, something caught my eye on the Fender Field Guide.
We all know and love the 5F1 Champ circuit, right?
Well....I noticed that the tube complement, and the majority of circuitry on the schematic for Fender's fabled unicorn, the 6G10 Harvard is the same.
There are some additional caps on the Harvard, as well some differently valued resistors. The Champ was cathode and the Harvard fixed. So what exactly is it that gave the Harvard a 10W output as opposed to the Champ's 5W, when it had the same tubes? As Roger Daltrey once sang, "I really wanna know..."
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Hawkeye Kane
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1847
908 posts
Jul 10, 2013
11:21 AM
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the champ has one 12ax7
the Harvard two?
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third times a charm!
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1847
909 posts
Jul 10, 2013
11:25 AM
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harvard must have a larger transformer as well
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third times a charm!
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timeistight
1287 posts
Jul 10, 2013
11:30 AM
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I doubt if that circuit could put out 10 watts. I think you've been misinformed.
According to Wikipedia:The later extremely rare or possibly even mythical 6G10 Harvard used a single 12AX7, 6V6GT and 5Y3GT and, it has been speculated, was simply a Princeton circuit which could be fitted in left-over tweed covered Harvard cabinets after Fender had re-launched the Princeton in a tolex covered version.
The Princeton circuit in question was rated at 4.5 watts.
Last Edited by timeistight on Jul 10, 2013 11:41 AM
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Jim Rumbaugh
884 posts
Jul 10, 2013
6:57 PM
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1) I don't see any fixed bias.
2) My bet is the cathode bypass capacitor in the first pre-amp. That will crank up the gain big time.
3) I don't see main B+ voltage for the Champ, is it also 360v ??
4) Are the output transformers the same? What about impedance match? A 4 ohm speaker will TRY to draw twice as much power as an 8 ohm speaker.
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theharmonicaclub.com (of Huntington, WV)
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tmf714
1834 posts
Jul 10, 2013
7:23 PM
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The Harvard stands alone in this one feature - a 6AT6 preamp tube. No other Fender amp used this tube. While the 12AX7 is a dual triode tube, the 6AT6 is a cute little single triode tube. Leo had designed the Vibrolux, but felt that another model between that and the Princeton was needed. So he simply removed the tremolo circuit of the 5F11 Vibrolux create the 5F10 Harvard. But there was an unused triode stage with the removal of the tremolo so the Harvard was designed with the single triode 6AT6 to eliminate redundancy. The Harvard is closely related to the Deluxe with three significant differences 1) plate voltages 2) 12" speaker (Deluxe) and 3) the Harvard lacks the tone recovery stage of the Deluxe. Had Leo used the redundant triode as the tone recovery stage, the 10w Harvard would had been too close to the 15w Deluxe.
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Rick Davis
2099 posts
Jul 10, 2013
7:41 PM
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No Tim, you are confusing two different Harvard models. The 5F10 had two 6V6 tubes and made 10 watts. You are looking at the 6G10 which had only a single 6v6.
The Mission Delta Sonic amp was modeled somewhat on the 5F10 Harvard: two 6V6 power tubes and a solid state rectifier. It uses the Harvard tweed cab.
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-Little Rick Davis
The Blues Harp Amps Blog
The Mile High Blues Society
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Last Edited by Rick Davis on Jul 10, 2013 7:49 PM
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jimr
52 posts
Jul 10, 2013
7:42 PM
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Some of the confusion is because Fender made at least two Harvards. 5G10 has a single 6V6 (so no phase inverter) and is cathode bias (schematic above). 5F10 has two 6V6 power tubes in push pull mode, cathodyne phase inverter,and is fixed bias.
Jim r
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HawkeyeKane
1874 posts
Jul 11, 2013
7:14 AM
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@1847
No, according to both of these schematics, they both use a single 12AX7 and they're both split.
@timeistight
Yeah, I read that Wiki article too.
@Rick
That would make sense. Once again, in my search to better acquaint myself with vintage amp history, the sources only serve to confuse me. Take a look at the Field Guide page on it. No disticntion between outputs or preamps.
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Hawkeye Kane
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timeistight
1288 posts
Jul 11, 2013
7:38 AM
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Anyway, it doesn't seem that the 6G10 amp was ever built. I've never heard of anyone finding one.
The 6G10 amp would have been a downgrade from the original Harvard, which produced 10 watts from a pair of 6V6 output tubes. Fender's model-change policy was to always upgrade to higher specs.
Last Edited by timeistight on Jul 11, 2013 9:15 AM
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Rick Davis
2100 posts
Jul 11, 2013
8:44 AM
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Tim, if you look at the Fender Amp Field Guide it does distinguish between the two models. It says the output is 10 watts without referencing which model, but it seems clear that since the single 6V6 amp is pretty much the Champ circuit it would make 5 watts like the Champ, and the 10 watt number would refer to the model with two power tubes. It fits the expectations we have for Fender amps of the era.
I agree with timeistight: I have never seen the 6G10 model with the single 6V6. When someone says "Harvard amp" I think of the 5F10 model.
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-Little Rick Davis
The Blues Harp Amps Blog
The Mile High Blues Society
Tip Jar
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5F6H
1651 posts
Jul 11, 2013
9:17 AM
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The 6G10 is rare, but they are out there, the circuit was also used in the White amp.
5F2A is <5W.
In essence, the 50's tweed Princeton turned into a 60's 6G10 Harvard...& was then dropped.
The 50's tweed Harvard, got tremolo & became the 6G2 tolex Princeton...at least, that's the way I make sense of it. ;-)
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Last Edited by 5F6H on Jul 11, 2013 1:44 PM
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tmf714
1835 posts
Jul 11, 2013
11:47 AM
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tmf714
1836 posts
Jul 11, 2013
11:50 AM
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There was a 6G10 Harvard made during its last years 1960/61 which is closest to the Princeton with its single 6V6 power tube. Speculation is that Fender was about to discontinue the Harvard as it was never a big seller. Leo never wasted anything, so he repackaged the Harvard in a Princeton cabinet to use up the supply of Harvard badges without building new cabinets. Leo was really frugal but practical
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Kingley
2872 posts
Jul 11, 2013
11:54 AM
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If my memory serves me correctly Pat Ramsey used Fender Harvard amps.
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HawkeyeKane
1878 posts
Jul 11, 2013
12:05 PM
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"Leo never wasted anything, so he repackaged the Harvard in a Princeton cabinet to use up the supply of Harvard badges without building new cabinets."
I can see that. Just strikes me as slightly odd that he'd feel the need to designate it with a seperate circuit number.
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Hawkeye Kane
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