Rift Tweed Vee (formally 'V-Front Super 5B4 Build')

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RiftAmpsRiftAmps Frets: 1136
edited May 7 in Made in the UK
As most of you know, I'm a bit of an enthusiast when it comes to vintage amplifiers. Anything pre-1980 really gets me going, and the older the better. I also do a lot of valve radio restoration and repair, some of the stuff I've worked on goes back to the 1920's. I stay away from TV sets though...flyback voltage can bugger off!

Anyway, Fender Tweed amplifiers have long been an obsession of mine and like most amp builders these days I offer a range of the most popular narrow panel designs - Champ, Deluxe, Pro, Super, Bandmaster, and Bassman. They're all fairly easy to do, parts are readily available, sound fantastic, and there are many good resources online if you need them. Want a high-powered Tweed Twin? Sure, let's do it. Need a Bassman in head format with a 2x12" cab? Go on then.

I also offer some of the older circuits, such as wide-panel and TV front models. These have proven to be very popular and I sell bucket loads of them. There clearly is a demand for these old designs and I'm not sure why no-one else offers them.

One of the amplifiers that I've always wanted to have a go at is the late 40s V-Front Super (pic below). It certainly has a unique look and sound, but information is scarce and finding one to play is even harder. Last weekend I realised that I actually had a few of the jigsaw pieces ready to go, and just had to find a way to get the rest.

So, this thread is going to document every stage of the research, build, testing, and completion of the V-Front Super, along with my ramblings and thoughts as we go along. I'm going to go full nerd on this, so brace yourself for lots of sums, measurements, and tedious back and forth. I'll include lots and lots of hi-res photos for those that just want to see the process.

I've also been following @WezV 's LP Prototype build on here, and as this would be an era-appropriate amplifier for a '51 Les Paul, it would be great to hear them together.


Rift Amplification
Handwired Guitar Amplifiers
Brackley, Northamptonshire
www.riftamps.co.uk
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  • WezVWezV Frets: 8253
    I am looking forward to it :)
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  • Jimbro66Jimbro66 Frets: 629
    I've booked a front row seat and a mega-tub of popcorn. Eagerly awaiting this thread :)
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  • RiftAmpsRiftAmps Frets: 1136
    edited May 7
    So a bit of history to start with...

    The V-Front Super (named because of the cabinet design) was actually the second iteration in this line. It started in 1947 with the Dual Professional - a 20w-ish 2x10" Tweed amplifier, with both instrument and microphone channels. It sat alongside the Professional model (a 1x15" combo) but this one had two speakers, hence Dual!.

    Each channel had its own 6SJ7 pentode preamp valve, before being mixed and fed into a 6N7 paraphase phase invertor, and then into a pair of 6L6G power valves. Each speaker had its own output transformer, mounted directly on the speaker frame.

    The Dual Professional name was shortlived, however, and Fender quickly changed it to Super. They used the circuit designation 5A4.









    Rift Amplification
    Handwired Guitar Amplifiers
    Brackley, Northamptonshire
    www.riftamps.co.uk
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  • RiftAmpsRiftAmps Frets: 1136
    edited May 7
    In early 1949, the circuit was revised to the 5B4 designation, and featured some big changes.

    Firstly, 6SJ7 pentodes were replaced by 6SC7 dual-triodes, again one for each channel but each half used for each input. The phase invertor was also changed to a 6SC7, but remained in paraphase configuration.

    Secondly, the dual output transformers were replaced with a single, larger unit - model #1848. This was a 6k6 25w unit with a single 4ohm secondary. The 1x15" Pro used #1846, which had an 8ohm secondary tap instead.

    Thirdly, the control layout was changed slightly.



    It is this version, the 5B4, that I'm wanting to recreate.
    Rift Amplification
    Handwired Guitar Amplifiers
    Brackley, Northamptonshire
    www.riftamps.co.uk
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  • RiftAmpsRiftAmps Frets: 1136
    edited May 7
    Where to start then?

    With any amplifier build, one of the main considerations is the chassis and with Tweed amplifiers it's quite difficult because no faceplates are used. The chassis are manufactured from 0.06" thick cold-rolled steel, chrome plated and then silkscreened. For the most popular circuits, chassis are readilly available but for something like this there's nothing out there. If you want something, you have to get it manufactured yourself.

    This is what I did for the Tweed 30TV (5A5 Pro), I had a run of 26 units manufactured at an eye-watering cost, but it was the only way to get them looking right, and built to the specs that I needed.

    Fortunately, the 5B4 Super uses the same chassis as the Pro, so I can use those! There is one slight snag, I had the chassis manufactured 1" longer than originals. Looking at the dimensions of the V-Front cab it shouldn't be an issue, but it might be a squeeze.

    The eagle-eyed viewer will notice a few differences, mainly the inputs aranged in a square rather than a line. I chose to omit the ground switch from the chassis as it's not needed in 2017.






    Rift Amplification
    Handwired Guitar Amplifiers
    Brackley, Northamptonshire
    www.riftamps.co.uk
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  • paulnb57paulnb57 Frets: 1100
    edited August 2017
    I can't pretend to understand the techy, nerdy bits, but I love this sort of thing, thanks for sharing, I shall follow with interest...I hate modern digital modelling stuff, what you are doing is real, proper, traditional, retro, right up my alley!
    Stranger from another planet welcome to our hole - Just strap on your guitar and we'll play some rock 'n' roll

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  • john_rjohn_r Frets: 62
    Will be following this one closely! 
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  • Winny_PoohWinny_Pooh Frets: 2585
    I'm curious as to what speakers are going in
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  • RiftAmpsRiftAmps Frets: 1136
    I'm curious as to what speakers are going in
    We shall get to that later :)
    Rift Amplification
    Handwired Guitar Amplifiers
    Brackley, Northamptonshire
    www.riftamps.co.uk
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  • RiftAmpsRiftAmps Frets: 1136
    edited May 7
    Next stop: Cabinet.

    I've learnt a great many things about the cabinet over the last week, some of which are very interesting indeed.

    As far as I understand it, the cabinet designed changed quite a few times over the 6 year run of the Dual Professional/Super, but it can be boiled down into two main eras:

    • Dual Professional, 5A4, 5B4 - Type 1
    • 5C4 - Type 2

    The Type 1 cabinet wasn't manufactured by Fender, but was outsourced to a local cabinet maker. It was 22.5" wide by 19.5" tall, and featured a sloped front - bottom depth (at the Vee) was 9.75", and the top was 8.5" - giving a 1.25" taper. The sides were 1" less than the vee depth - 8.75" and 7.5" respectively. This meant that not only were the sides tapered, but the Vee was too.


    The Type 2 cabinet was manufacturered in house by Fender, and unlike the Type 1, it had no taper at all. Both the sides and Vee were straight (much like the Watkins Dominator). It was 1" shorter but also 1" wider 23.5" x 18.5". The depth was 8.25" at the sides and 9.5"at the Vee. On this cabinet, the Vee is 0.25" prouder than Type 1.


    Type 1






    and Type 2






    For this build, I'll be going with the Type 1 cabinet.

    Rift Amplification
    Handwired Guitar Amplifiers
    Brackley, Northamptonshire
    www.riftamps.co.uk
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  • RiftAmpsRiftAmps Frets: 1136
    edited May 7
    The speaker baffles on this cabinet are interesting, as they are mounted to the cabinet using metal brackets on the outer side, and directly to the metal strip in the centre





    I'm particularly keen to avoid cabinet buzz and rattle, so we'll be using cleats to mount the baffles to the cabinet instead. This is still an era-appropriate method but will provide a much more stable platform. The metal strip on the front will no longer have a structural purpose, so it'll be made from polished aluminium and attached to the front with countersunk stainless steel screws.
    Rift Amplification
    Handwired Guitar Amplifiers
    Brackley, Northamptonshire
    www.riftamps.co.uk
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  • RiftAmpsRiftAmps Frets: 1136
    edited May 7
    So, whilst I'm waiting for the cabinet to be made, we can start to have a look at the circuit.



    The picture above shows the layout for the 5B4 Super, but there is no schematic available that I can find. We can however, look to the 5B5 Pro for inspiration as we know the circuits are almost identical. There is a schematic for that amp.



    The most obvious difference is the output transformer and speaker config, but the sharp-eyed viewer will notice that the Pro amp has four 20uf 450v power supply electrolytic caps, whereas the Super has only 3. On the Pro, the reservoir cap is 2x20uf in parallel, giving a toal of 40uf. On the Super, it's just a single 20uf. This will give a slightly higehr and cleaner B+ voltage on the Pro, but not by much. In my build, I'm going to stick with the Super's config, and can always up the filter stage to 33uf or 47uf if I feel it needs it.

    Apart from that, I can't spot any other differences.

    Rift Amplification
    Handwired Guitar Amplifiers
    Brackley, Northamptonshire
    www.riftamps.co.uk
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  • RiftAmpsRiftAmps Frets: 1136
    Power Transformer


    The PT is listed as #6516, and the layout details that it has a HV 700v CT secondary (350v-0-350v), capable of supplying 140mA of current.

    Having experienced problems with Fender schematics/layouts before, I think it would be wise to workout exactly what we need and then comparing it.

    So, how much B+ do we actually need?

    Starting with the 6L6G power valves, the layout show a combined cathode voltage (Vk) of 24v, and a shared cathode resistor of 250ohms.

    Ohms law states that current (I) is voltage / resistance.

    So 24v / 250ohms = 96mA for both valves.

    Note - this is the Cathode Current (Ik) which is the sum of both the Anode Current (Ia) and Screen Current (Ig2) flowing through both valves.


    The 3 x 6SC7 preamp valves will typically draw between 1-3mA per triode, of which there are 6 in total. So worst case is 6 triodes x 3mA = 18mA.

    96mA + 18mA = 114mA - Somewhere short of the stated 140mA. Infact the PT is rated for 23% more B+ current. Amazingly, this is not as uncommon as you might think.


    What about heater current?

    Easy, we need two separate heater windings, one for the rectifier valve, and the other for the rest.


    The rectifier valve (5U4) needs 3A at 5V

    The rest are all 6.3v, rated as follows:

    2 x 6L6 at 0.9A each (1.8A)
    3 x 6SC7 at 0.3A each (0.9A) 


    So we need a 6.3v winding capable of delivery 2.7A.


    Rift Amplification
    Handwired Guitar Amplifiers
    Brackley, Northamptonshire
    www.riftamps.co.uk
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  • RiftAmpsRiftAmps Frets: 1136
    edited May 7
    Progress on the cabinet...




    Rift Amplification
    Handwired Guitar Amplifiers
    Brackley, Northamptonshire
    www.riftamps.co.uk
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  • RiftAmps said:
    I've also been following @WezV 's LP Prototype build on here, and as this would be an era-appropriate amplifier for a '51 Les Paul, it would be great to hear them together.
    Man Date. 
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  • paulnb57paulnb57 Frets: 1100
    Nice bit o cabinatery
    Stranger from another planet welcome to our hole - Just strap on your guitar and we'll play some rock 'n' roll

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  • WezVWezV Frets: 8253
    You need to add this cab choice to the line up for a few more models.  How long is it going to be until someone asks for a WEM dominator style
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  • RiftAmpsRiftAmps Frets: 1136
    WezV said:
    You need to add this cab choice to the line up for a few more models.  How long is it going to be until someone asks for a WEM dominator style
    I plan to offer the V-Front cab with any of my Tweed circuits...eventually. This first cabinet is somewhat of a prototype to see how things go as it's built to vintage spec, I might have to tweak the dimensions to
    accomodate different sized transformers etc. Once we've got the design where it needs to be we can then offer it in numerous Tolex/Grille options.
    Rift Amplification
    Handwired Guitar Amplifiers
    Brackley, Northamptonshire
    www.riftamps.co.uk
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  • Lovely work, are there any sound clips on you tube of these amps, I'd be interested in how they sound compared to the normal fender stuff 
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  • RiftAmpsRiftAmps Frets: 1136
    Lovely work, are there any sound clips on you tube of these amps, I'd be interested in how they sound compared to the normal fender stuff 
    The best one I've found is this



    Also, I think that all of ZZ Top's "Antenna' album was recording using V-Front Supers and Tele/Esquires.

    Rift Amplification
    Handwired Guitar Amplifiers
    Brackley, Northamptonshire
    www.riftamps.co.uk
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  • RiftAmpsRiftAmps Frets: 1136
    edited May 7


    I've just had an e-mail back from a friend in the States who owns an original 5B4. I had asked him to compare the voltages on his amp with those found on the layout to see how accurate they were. With the correct 117v AC mains input he measured the readings in Red.

    Now, from experience the voltages on the older Fender layouts/schematics shouldn't be taken as gospel...they were working engineers drawings and who knows what operating conditions those measurements were taken under. Ohms Law will tell you that some of the voltages found are either impossible, or highly improbable (see 6G2 Princeton). It's usually best to find an original example and take your own readings under real operating conditions.

    Anyway, the voltages in Red match others (+/- 5%) found online in forums and magazine articles, so it's probably safe to say that they are true. Now I can start to do some more accurate calculations.
    Rift Amplification
    Handwired Guitar Amplifiers
    Brackley, Northamptonshire
    www.riftamps.co.uk
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  • Thanks I'll have a listen
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  • RiftAmpsRiftAmps Frets: 1136
    edited May 7
    So, onto the build proper...


    Below shows the eyelet board on my super hi-tech 'Board Population Rig' - this allows me to drop the components into place and gravity holds them there whilst I solder in place - saves bending the component legs over underneath the board.






    Here, the filter pack is populated in place. 3 x 22uf 450v electrolytics and 2 x 10k 2w metal oxide resistors. Hole in the middle is a mounting point to chassis. The board will sit on 1/4" standoffs.






    The completed board. Annoyingly, I was out of stock of the 6L6's cathode bypass cap (25uf 63v) so left a space to add in when the delivery arrives.

    I went for my stock Jupiter Yellow tone caps - a huge improvement over Mallories or Orange Drops.

    Next job is to make the underboard connections, clean off any solder flux, and attached the flying leads.




    Unfortunately, the build must stop here whilst I move into my new workshop. Watch this space...

    Rift Amplification
    Handwired Guitar Amplifiers
    Brackley, Northamptonshire
    www.riftamps.co.uk
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  • RiftAmpsRiftAmps Frets: 1136
    edited May 7
    The cabinet arrived a few weeks back, but due to the workshop move, I haven't had much chance to do anything.

    Speakers

    The original 5B4s were loaded with Jensen P10R Alnico speakers, and for this amp, I definitely wanted to stick with Alnico, despite being so expensive. I went for WGS G10As, an American voiced driver with a 1" voice coil and 40oz magnet. SPL is 97db and the resonant freq. is 82Hz. Whilst a little overpowered for this amp at 75w a piece, tonally they're spot on without that awful papery, fizzy cone distortion when driven hard.


    The transformers are due to arrive next week, so can finally make progress with the chassis build.




    Rift Amplification
    Handwired Guitar Amplifiers
    Brackley, Northamptonshire
    www.riftamps.co.uk
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  • 77ric77ric Frets: 74
    That cabinet looks amazing. Can’t wait to see the complete build. 
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  • Jimbro66Jimbro66 Frets: 629
    Did this project ever complete @RiftAmps?
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  • RiftAmpsRiftAmps Frets: 1136
    Jimbro66 said:
    Did this project ever complete @RiftAmps?
    Completely forgot about this thread!

    I shall update it tomorrow :)
    Rift Amplification
    Handwired Guitar Amplifiers
    Brackley, Northamptonshire
    www.riftamps.co.uk
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  • Jimbro66Jimbro66 Frets: 629
    RiftAmps said:
    Jimbro66 said:
    Did this project ever complete @RiftAmps?
    Completely forgot about this thread!

    I shall update it tomorrow :)
    Thanks. I think there was quite a lot of interest in it at the time..........
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  • lonestarlonestar Frets: 1721
    I just caught up with this. Amazing build, Chris! 
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  • merlinmerlin Frets: 1158
    edited March 12
    RiftAmps said:

    I've also been following @WezV 's LP Prototype build on here, and as this would be an era-appropriate amplifier for a '51 Les Paul, it would be great to hear them together.

     I am the proud owner of the WezV prototype Earth 2 '52 so I am going to have to call dibs on this one (if you're moving it on after the build Chris @RiftAmps) ;.... I have a strong suspicion that we'll be talking deep sonic joy here! 
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