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Old 4th Sep 2019, 3:55 am   #1
retailer
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Default Fender amp copy

Following on from my Vox AC15 copy I built late last year I've started to build a Fender Deluxe Reverb copy, I like to build stuff and at least I know once it is in the hands of my son it won't end up in a skip after I move on to the next life. As with the Vox copy I did everything from scratch, the chassis came from an old road sign and was bent up on my homemade folder, the hardest part was scraping all of the old paint off, after trying a heat gun and paint stripper I found the best way is to burn it off out in the open, the charred residue is then easily sanded off, an added bonus is that this also anneals the Al so it bends easier and put less strain on my folder - if I try 2mm Al 57cm
wide that has not been annealed the folder flexes in the middle.

I wound the transformers (3 of) and choke some months back as I knew this project was coming up, the output transformer was wound without a bobbin on a cardboard former using my homemade winder - the old way with paper
insulation between each layer, the insulation provides a nice smooth flat surface for the next layer of wire. All of the hardware valve sockets etc have been reclaimed from old junked gear.

The turret board did not take that long the most tedious part was riveting the turrets, I had 99% of the parts on hand in my spares drawers and only needed one trip to Jaycar for a few resistors. Just about all of the wiring has been done and it won't be long before I give it a bench test.
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Old 4th Sep 2019, 5:42 am   #2
joebog1
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Default Re: Fender amp copy

I must say thats a VERY proficient job !!
I am especially envious of the quality of the parking sign reclaimation.!! .

That power transformer looks about twice the size of the "standard" Fender unit!! (which I have always found "piddly" to be generous)
Nice big fat flux band will only help a super low noise model.

Congratulations!!

Joe
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Old 4th Sep 2019, 6:44 am   #3
mole42uk
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Default Re: Fender amp copy

Now there’s a project and a half! It looks just right, I hope it sounds right too!
What speakers are you planning to use?
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Old 4th Sep 2019, 8:42 am   #4
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Default Re: Fender amp copy

I love your make do and mend approach, refreshing.
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Old 4th Sep 2019, 3:04 pm   #5
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Default Re: Fender amp copy

The build went reasonably smoothly and was able to do a bench test this afternoon this was when I had a senior's moment that lasted the rest of the day. What should have been 21 odd watts output measured at just 4 watts, all of the valve voltages measured with in spec, I had already checked over the wiring before testing and did find the odd mistake so I was scratching my head and starting to doubt my output transformer, the amp not only maxed out at around 4 watts but also the scope test sinewave did not clip nicely but at around 4 watts it turned suddenly in a horrible jagged line resembling a grimacing mouth.

I tried a known good factory made output transformer - sat it on the bench next to the amp and hooked it up using croc clip flying leads - not quite 20 watts (wrong impedance) but good enough to firmly point the finger and my homebrew output transformer or so I thought. I cursed myself silently mainly because the transformer mounting bolts were under the turret board, as the leads were already unsoldered and before I started on the process of removing the turret board I gave the transformer a check over with the ohm meter - all good - next with the signal gen into the primary just in case I had wired the two primary halves out of phase - then an insulation test at 1000 V (max for my BM10) all tested good, so I clipped it back into the circuit with the croc clip flying leads give it another test, I didn't however use the speaker chassis socket as it was hard to get to but used a spare socket I had lying on the bench - perfect, sinewave started to clip at just under 22 watts, at this point the penny should have dropped, but don't think about it I thought just rewire it back into the circuit, once done I gave it a quick test and sure enough back to 4 odd watts output, how could this be nothing had changed, I was out of ideas, the transformer had to come out. I started to unsolder the secondary leads first and I noticed that I hadn't connected the mains ground lead to the chassis - maybe that was it, a voice inside my head was saying you're grasping at straws here but not listening I clipped it to the chassis with a flying lead and as the secondary leads were unsoldered I quickly clipped them to the spare 1/4inch socket that was lying on the bench and powered up the amp for a quick test, it came up perfect 22 odd watts, this is the second time the penny should have dropped. I was dumfounded and frankly a bit disbelieving, thinking that can't be it, must be something else. While I was poking around I accidently bumped the speaker socket that was hanging in mid air, it touched the chassis and the nice sinewave on the scope dropped to almost zero, finally the penny dropped.

I have a dummy load built into a homemade power meter - a cast Al project box 3 position switch for 4,8 and 16 ohms an AC voltmeter/power meter mounted on the front and a long lead ending in a 1/4 inch jack, I had also fitted a BNC socket on the side so I can connect the dummy load resistor via a BNC lead to one of my scope inputs saves me having to use croc clip leads all over the place. With the 1/4 inch jack unplugged and disconnected from the amp I measured around 3.5 ohms between the 1/4 inch jack tip and the amp chassis, so with the transformer correctly wired into the amp and speaker socket my dummy load presented a near enough short to the amp rather than the 8 ohms I had it set to, clearly I had wired my dummy load incorrectly and had transposed the earth an active wires so the jack tip was connected to the BNC earth which was connect to the scope which was plugged into the mains, the signal gen, also plugged into the mains was connected to the amp input socket. Reversing the connections at the 1/4inch jack, fixed the issue, with everything connected I gave the amp another test it was all good and ready for an actual test by the end user.

The old road signs are cheap if you pick them up from the salvage yard $5 ea nice and thick 2mm and most are good size the only down side is they can be a bit warped around the holes and that paint which is not actually paint but vinyl sticker, the vinyl comes of with a heat gun but the glue sticks like you know what to a blanket so the propane torch is the best thing.

I have a number of speakers available to use and it will depend a bit on how they sound to my son he'll have to make the choice, I have an old mid 70's Celestion Green Back, an old Vintage 30, a pair of Rola C12P speakers and a generic 12inch Chinese music instrument speaker that looks like a copy of the Vintage 30. I also have a old pair of Celestion 10's that I think came out of an old Marshal 4x10 cab.
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Old 9th Sep 2019, 5:10 pm   #6
ColinTheAmpMan1
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Default Re: Fender amp copy

I see that you have the mains transformer, choke and output transformer aligned correctly (original mains transformers are drop-through, the choke and output transformers are top-mount with the cores parallel, but the reverb transformer would be better at a 45-degree angle to prevent coupling.

I would probably look for a speaker that is a bit more "American" - Jensen speakers are now made in Italy, if I remember correctly.

I have to admire your attitude to making clones of classic amps. I started to make a copy of a Fender Deluxe Reverb some years ago (I still haven't completed it, either) but eventually baulked at bending my own chassis. I am also adding some modifications - there is a "middle" control on the vibrato channel, the reverb circuit has "tone" and "dwell" controls a la Fender stand-alone reverb unit and I have also added a "presence" control. I do hope I can complete it before I keel over!

Colin.

I hope you at least used carbon film resistors, or better carbon composition. I completely "refurbished" my Vox AC30 years ago and used metal-film resistors - not a good idea, as a certain amount of the old Vox mojo was lost. I am also working on putting this mistake right, too.

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Old 11th Sep 2019, 2:45 pm   #7
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Default Re: Fender amp copy

I thank all for the kind comments that have been made.

The only extra I added was a bright switch to each channel, the thought was there to also add a "mid" to the tone stack, I believe the reissue Fender amps have this, but by the time I was thinking a bit more seriously about it I had already drilled the holes for the controls, the AB763 circuit seems to be regarded as the pinacle in Fender amps I'm quite sure my son will learn to live without, he has managed with only a top cut tone control on the Vox with no complaints - I was surprised to learn he had loaned his AC30CC to a friend and the AC15 copy had become his gig amp.

I used metal film rather than carbon film resistors I know they do not look period correct and as you say may affect the vintage style tone but put simply I have a good stock of them and want to use them up. The same comments go for the speaker, it would be nice to go all out with a full blown real copy and get an Oxford or Jensen but I really want to use up some of the gear I have collected over the years, if my son wants an 'American' sounding speaker he'll have to fork out for it himself.

I didn't have a small 'donor' to rewind for the reverb driver transformer - that coupled with the fact I made the chassis 2 cm smaller so it would fit in my folder meant I really did not have the room the turn the transformer at 45deg - my son came over and we gave it a short test and so far no issues with hum on either channel fingers crossed it is like that once it is finished and he cranks the volume.

I picked up the pine planks for the cab today, hopefully I don't have the same router issues when it comes time to make the finger joints, the AC15 cab gave me a lot of grief. I have some fire engine red vinyl, white piping and black grill cloth - I plan to use them on the cab.
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Old 11th Sep 2019, 5:53 pm   #8
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Default Re: Fender amp copy

Wow, that looks brilliant. What a great piece of work indeed.
Its my intention to build a clone AC15 too as I have already bought a JMI one a while back. However, its back in the queue as I'm working on a an old Shaftesbury (threads on here), an old Triumph Leo 5 watt and then a Marshall clone of either the 1930 Popular or I am now thinking of the 1958 (mini bluesbreaker).
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Old 13th Sep 2019, 10:43 am   #9
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Default Re: Fender amp copy

I checked out your Shaftesbury post looks like you are well on the way to getting it going, restoring old gear can be quite rewarding.

Some years back while I was at a salvage yard I noticed what looked like a guitar amp chassis in one of the electronics recycle bins I jumped in and retrieved it and $5 later it was mine - it turned out to be an Electronics Australia kit built 60W head Playmaster 117 running a pair of 6DQ6's in the output, it was (and still is) in a sad state most noticeable was the odour like stale urine. My guess is that the owner was frustrated at being unable to get it working so the band members all lined up and emptied their bladders onto it. The amp designers had used the Fender trick of using one of the unused valve socket pins as the terminating point for the grid resistor - forward a few years and the new crop of valves used that pin for a second screen or anode connection (I forget which) so a healthy 180 odd volts was fed to the grid resulting in almost instant red plating on powering up.

It is all there and I did getting it working correctly including the tremelo but one of these days I'll do a full restoration, strip it back to bare chassis have it re-plated and rebuild with all new period correct capacitors and carbon resistors.
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Old 13th Sep 2019, 11:49 am   #10
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Default Re: Fender amp copy

The Playmaster amps are VERY similar to Goldentones. Both are aussie design and both very capable amplifiers. A simple and very neat power supply design using a centre tapped transfomer, BUT a bridge rectifier gives a nice strong 350 odd volts for the plates, and a nice 175 volts for screens. Both amps tend to be " VERY LOUD" with excellent lead characteristics, especially with Fender Telecaster, or Maton Firebird guitars.

Ideally you need Rola Alnico's to obtain the best tones, but either way you have a nice amp to restore.

I am especially fond of both designs, Goldentone would be a tad on the winning side however.

Joe
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