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Post subject: Original Bassman Amp: which is the correct circuit?
Posted: Sat Jul 15, 2017 2:22 am
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Hi there,
I am new to the forum and hope to be at the right place for the question I have.

First, however, a quick introduction: I live in Southern Bavaria and have been a fan of Fender guitars and (even more so) amps ever since I could afford my first good amp (a Twin Reverb bought new in 1974). Since then the household has never been without a Fender amp (although I do enjoy other amps, as well). A am an avid amateur guitarist and besides the music itself also have a pronounces interest in the technical side of the electric guitar and the associated amplification. My professional background is audio engineering, instrumentation and intellectual property.

Now, on to my question:
I am trying to find the schematic for the original late 1951 or early 1952 TV-front Bassman. Supposedly, it has the designation 5A6 .... and it can be found all over the internet. Except that obviously, the circuits published on the internet which I found (e.g. http://vintagefenderamprepair.com/wp-co ... ematic.pdf ) are not those of a Bassman since they sport 3 inputs and two volume controls (rather than the two inputs and single volume control the Bassman had). Also, this alleged 5A6 circuit shows two speakers (rather than one) which are moreover connected to two separate windings of the output transformer (or maybe it means to indicate TWO output transformers).

Therefore I conclude that this schematic is NOT that of the original Bassman Amp, and my question is whether any body here can point me to the correct circuit?

Many thanks in advance and a great weekend to all!

P.S.: The circuit found on the internet under the 5B6 designation very much seems to be a correct Bassman schematic corresponding to all other available info. I connect the 5B6 to the wide-panel version available in 1953 which apparently has the same structural design as the TV-front amp. There probably were not big alterations between the 5A6 and the 5B6 but it would be nice to have a schematic of the first Bassman.


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Post subject: Re: Original Bassman Amp: which is the correct circuit?
Posted: Fri Aug 11, 2017 1:24 pm
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Is it the good one ?

http://ampwares.com/schematics/bassman_5b6.pdf


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Post subject: Re: Original Bassman Amp: which is the correct circuit?
Posted: Fri Aug 11, 2017 5:58 pm
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AFAIK, the first "Bassman" amp was really a re-labeled TV Front Pro (5A5). Maybe, with some coupling cap changes. I'll have to look at this when I get off from work.

The confusion in the output stage, is the use of FIELD COIL magnets in these very early Fender amps. The speaker's fixed magnets are electromagnetic, in place of ceramic or alnico. Charged from the power supply. These form the set magnetic field. The voice coil is wound like ceramic or alnico speakers, in the middle of this FIELD COIL magnet.

Early schematics make it look like there might be two speakers. I think there is only one 15-inch FIELD COIL speaker.

Anyhow... 5A5 schematic with the FC field speaker included.

http://ampwares.com/schematics/pro_5a5- ... rected.pdf


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Post subject: Re: Original Bassman Amp: which is the correct circuit?
Posted: Fri Aug 11, 2017 11:26 pm
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Dear Stratele 52 and BMW2002ti (very nice and stylish car, by the way - one of my "dream cars" as a boy!),

thank you so much for your help and input! Let me comment:

@stratele:
this is certainly a good one! Whether it is THE good one (i.e. the one of the very first Bassman), I don't know. It does look like what I would expect, anyway, but then it seems to be exactly what I know as 5B6 schematic, and when I try to store the file it even says bassman_5b6 in the file name. So is may or may not be the first bassman schematic, because it may be that a 5A6-version was not built in any numbers worth mentioning, and the 5B6 was the first real production Bassman. In that case the TV-front- and the wide-panel-versions would have differed merely in the cabinet style and would have electronically been the same. That would be my working theory for the moment.


@ BMW2002ti:
I think your comment that the first Bassman amps were TV-front Pro Amps is most interesting. It connects well with what Teagle & Sprung write in their book "Fender Amps - the first 50 years": "The first P-Basses were reportedly shipped with TV-front Pros." I have little doubt that the first Bassman amp was VERY close electronically to the Pro especially in the output stage - however, there was a major difference in the input circuitry on that the Pro had two input channels with two volume controls while the Bassman had only one channel with a single volume control. So there must have been a different schematic for the Bassman - whether there ever was a true 5A6 version is unclear to me (see what I wrote above to stratele52).

The other most interesting aspect you mention is the field coil speaker. Do you know whether Fender actually used field coil speakers as "late" as 1952? I guess this speaker type was at least not consistently used any more by the early 50's - Tom Wheeler does mention however in his book "The Soul of Tone" that in 1951 Pro Amps occasionally came with a field-coil speaker. The photo of the early Bassman (it says '52-'54 in the caption) shown in the Teagle & Sprung book depicts a speaker which looks rather "modern" - I can see no field coil connection (although I think I can see the extra wires necessary in the photo of the Dual Professional/Super amp with the two output transformers) . I would be most interested and generally curious about the field coil speaker use (which I associate more with the 1930's and the 1940's). None of the schematics I can find of early Fenders show any of the wiring necessary to power the field coil which makes me wonder - given that in other respects the drawings are highly complete. The drawing you provided is the first I see including the field coil so it's a great find and I very much appreciate you supplying it! If you can point me to further info I would be most grateful!

Kind regards and great weekend to all!


Last edited by OrangeJBL on Sun Dec 03, 2017 2:40 am, edited 1 time in total.

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Post subject: Re: Original Bassman Amp: which is the correct circuit?
Posted: Sat Aug 12, 2017 12:04 am
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OrangeJBL, I have worked on very early Fender amps that had field coil speakers. Seems there was a lack of affordable (non hi-fi), fixed ceramic magnet speakers, 15-inch speakers immediately post WW2. But, there was a lot of field coil types.

These definitely lack the bass punch of good fixed ceramic or alnico magnet speakers. Plus requiring bigger PT to handle the extra current draw of the EM magnets.

:)


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Post subject: Re: Original Bassman Amp: which is the correct circuit?
Posted: Sat Aug 12, 2017 12:14 am
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Again, many thanks for your input - and for the promptness of your reply! It is great to get this info from an expert who has actually worked on these old amp!

Best regards!


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Post subject: Re: Original Bassman Amp: which is the correct circuit?
Posted: Sat Aug 12, 2017 9:15 pm
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You are welcome! Do you have one of these old Bassman? Very cool amp.

:)


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Post subject: Re: Original Bassman Amp: which is the correct circuit?
Posted: Sat Aug 12, 2017 11:11 pm
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(Un-) fortunately :wink: , I do not own one of these historic amps - my interest here very much an academic one.

We have a group of scientist here who really try to get behind what makes the electric guitar and the associated processing (amps, effects, etc) tick. We try to weed through all the hype and mystique to find out e.g. what actually is so special about those legendary amps. There is a reason some of them are so wonderful but a lot of what is being stated on various media does not make technical sense. We seek to fill that gap.

In autumn, we have a meeting of the members of our little association - a bit like a conference - and one of the presentations is about the Bassman and how it evolved, including the evolution of the Marshall amp up the late 1960's. That is why I am trying to get the info on the very first Bassman. The later ones are very well documented, as are the Marshall amps.

Our association is just in the process of setting up a website which will also include a (growing) English language section. As soon as that is ready to go public, I shall be back and post a link.

For now, have a great Sunday! Take care & kind regards!


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Post subject: Re: Original Bassman Amp: which is the correct circuit?
Posted: Mon Sep 18, 2017 9:17 am
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OrangeJBL wrote:
(Un-) fortunately :wink: , I do not own one of these historic amps - my interest here very much an academic one.

We have a group of scientist here who really try to get behind what makes the electric guitar and the associated processing (amps, effects, etc) tick. We try to weed through all the hype and mystique to find out e.g. what actually is so special about those legendary amps. There is a reason some of them are so wonderful but a lot of what is being stated on various media does not make technical sense. We seek to fill that gap.

In autumn, we have a meeting of the members of our little association - a bit like a conference - and one of the presentations is about the Bassman and how it evolved, including the evolution of the Marshall amp up the late 1960's. That is why I am trying to get the info on the very first Bassman. The later ones are very well documented, as are the Marshall amps.

Our association is just in the process of setting up a website which will also include a (growing) English language section. As soon as that is ready to go public, I shall be back and post a link.

For now, have a great Sunday! Take care & kind regards!


This is a very interesting post. I will stick around to see the final link
mud


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Post subject: Re: Original Bassman Amp: which is the correct circuit?
Posted: Sun Dec 03, 2017 1:36 am
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It's been a long time now, but I promised to post the info about the info about the new website of our association (named "GITEC") here. As I have stated above, we have a group of scientist here who try to get behind what makes the electric guitar and the associated processing (amps, effects, etc) tick. We try to weed through all the hype and mystique to find out e.g. what actually is so special about those legendary amps and pickups. There is a reason some of them are so wonderful but a lot of what is being stated on various media does not make technical sense. We seek to fill that gap.

If you are interested, take a look at:

https://gitec-forum.de/wp/

We now have an English language section:

https://gitec-forum.de/wp/en/

we hope it continues to grow - albeit slowly because we are all volunteers and do this work "on the side".

In any case: thank you for your interest, and if you have any questions, do write to us via the message function on our website.

Have a great Sunday and pre-Xmas time!


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Post subject: Re: Original Bassman Amp: which is the correct circuit?
Posted: Sun Dec 03, 2017 9:12 am
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Nice site! I like fast, vintage Bay-Em-Veys, too!

Image

Image

Good luck with your new site!

:)


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Post subject: Re: Original Bassman Amp: which is the correct circuit?
Posted: Tue Dec 05, 2017 12:45 pm
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What a nice reply - in a number of ways! Thanks so much! Is that Beamer yours? Those were the coolest cars when I was a boy - that one in the pic only beaten by the 2002 TII (double "i") ...


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