Dr d wrote:Just getting back to the HRM values, I started with a 500k bass pot in my recent Bluesmaster build and felt the OD was lacking something. I then changed it up to 1Meg and ,wow, what a difference. Still set @ 75K, but had more depth and character in its tone. I am not sure it is as simple as just using the nearest value needed for adjustment. When in doubt I always trust that HAD had a good reason for chooseing the values he does. Just my opinion, of course.
IMO sounds like your first trimmer was defect or of poor quality.
If you set your trimmer @70k, you don't 'use' the rest of the trimmers carbon, which is simply shortet so to speak.
Therefore, it shouldn't matter whether you use a 100k, 500k or 1m trim as long as you set it at 70k. The difference is the carbon's quality and/or the viper's connection/interaction with the carbon.
KT66 wrote:The most specific reference that I could find is from Gerald Weber's A Desktop Reference of Hip Vintage Guitar Amps on page 55 where he states " Contrary to popular belief, Leo Fender did not design the Bassman circuit. The circuit was actually patented by AT&T and Western Electric in 1948 and later licensed to Fender Electric Instrument company."
Although, this is admittedly rather vague as to which specific Bassman circuit was licensed and still leaves in question the origins of the so called FMV ( Fender Marshall Vox) tone stack. If you accept that terminology to mean that that type of tonestack is common to all 3 types of amps in its popular FMV nickname ( and you very well may not, and I can see why, as the Vox stack has a fixed mid resistor and the bass pot grounding "error" : http://members.optusnet.com.au/~glen325/topboost.html then I guess we should call it the GFMV stack because Gibson first used it in the GA-77 and GA70 in 1954 - predating the 5F6-A by 4 years.
The GA70/77 tone stack is close, but not the same. It's a two-knob control, as shown below, rearranged to make it look as similar as possible. The Gibson amps are overall very similar to the 5F6-A, so much so that they could have a common ancestor. However, besides the difference in the tone stack, the 5F6 also has a LTP PI instead of a cathodyne. This wider circuit genealogy is for a different thread, but if Gibson and Fender both started with some common circuit (this 1948 Western Electric?) and arrived at the different configurations we see, then I still think Fender was first with this three-knob treble-middle-bass stack, in a guitar amp, at least.
KT66 wrote:I didn't give the circuit it's name, HAD did. He used the Marshall plexi stack as a post overdrive tone shaping circuit, and called it the HRM.
Does anyone know for sure what HAD called it, i.e., what HRM stands for? Not arguing, just curious... Is there any existing documentation from HAD?
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martin manning wrote:
I've heard it mentioned that Fender used circuits developed by Western Electric before, but I have never seen anything specific... do you know of any references?
Back when tubes were a new thing the manufactures put out books with specs and example circuits and the formulas to calculate the correct component values.
My understanding is that in the case of the 5F6-A Fender used the Western Electric handbook. The amp was not designed by Western Electric, but the circuits and formulas all came from that book.
