Other Amps

I’m gonna make a Supro!

1

The thread on amp kits put me onto the Watts site - whoever linked to that THANKS! It's odd - I had seen that site before about a week earlier when looking for cloth covered wire, but not really looked at the kits.

Anyway, I just ordered one of these: http://tubeamplifierparts.c...

A Supro 24 style amp. It seems to have most of the parts I would have chosen myself. The only things I might have changed are the pots (I like PEC) and the coupling caps (I like Sozo over Mallory). But I think I'll just build it the way it comes. Original Supro amps are a rarity where I live so this will be interesting to try.

Has anyone else tried the Supro 24 kit?

2

Jimmy, please post a build thread for us geeks!

3

Least we know they'll be built much better than the originals!

4

That's a good choice... I still say 1960-1966 Supro sounded damn near as good as Fender.

5

Haha! Well ok, I will post some pics as i go. I have emailed them to find out how wide the chassis is. I wonder if I have a cab which it might fit?

I don't really need any more amps, but I thought the price seemed reasonable and I just love to build an amp. I have never played a Supro, so I won't be able to comment on how authentic the tone is. But I can take it into my local guitar shop and compare it with the new ones when it's built i guess. Never used those power tubes before either.

6

Oooh this looks like fun. Enjoy the build!

7

You might want to convert this to use 6V6 power tubes instead of 6973. Finding decent 6973 power tubes is a real headache these days. Vintage ones cost $50 a piece. The modern Electro Harmonix one positively suck. You'd probably have to order 6V6 sockets and rewire things a bit at the sockets.

Before you scream "Heresy!" be aware that there are adaptors available so you can run 6973 tubes on a 6V6....but not the opposite. So making the amp able to run 6V6 power tubes will make your life easier and more versatile without burning any bridges.

http://www.ebay.com/itm/ONE...

9

Well that sucks! I have EH tubes on the way. I have only used their 12ax7s before - and that was briefly. Before they crapped out. EH = Sovtek anyway.

I am looking forward to hearing the 6973 - that was part of the appeal of building this amp. The kit hasn't arrived yet. Living in Australia makes these things take ages, but then I have grown good at waiting. I already have 6V6 amps - in fact I have been playing my beefed up tweed Deluxe a lot lately as it's such a sweet sounding amp.

Buying NOS these days is such a crapshoot.

10

The Electro Harmonix 6973 seems to me to be some Russian tube designed for some purpose other than audio that was found to be able to tolerate the higher plate voltages so it's on spec. But they sound very muddy and dull in my Magnatones. Vintage 6973 tubes like the RCA sound great but are so expensive. In my opinion they aren't THAt different than more common EL84 or 6V6 in terms of sound to be worth the trouble in a guitar amp (hi fi audio might be a different story)

You might be able to get by with 6CZ5 power tubes in this amp given the plate voltages on that schematic. They're still pretty cheap NOS and sound great.

6CZ5 tubes have the same pin out as 6973 but can only handle around 350 volts on the plates...maybe 375. (A 6973 was designed to handle 450v) Your schematic calls for 350v 6CZ5 tubes were used in Magnatones at 375v with no issues so you could be o.k. with these. They cost about $20 online NOS.

6CZ5 tubes are often marketed as a "fake 6973" or a "6973 substitute"

http://www.ebay.com/itm/Pai...

Personally though I'd probably just rewire the power tube sockets to take EL84 tubes and be done with it. I think EL84 tubes sound great.

11

BTW if you wanted to convert this to EL84 you basically just have to solder 4 wires to different pins on both power tube sockets:

instead of pin 3/6 connect that wire to pin 2

Instead of pin 7, connect that wire to pin 3

Instead of pin 9 connect that wire to pin 7

Instead of pin 1 connect that wire to pin 9

Leave the filament wires as they are.

And that's pretty much all there is to it.

12

Thanks GC - really appreciate it. I used to think EL84s were thin sounding. But then I had a Badcat Cub IIR for a while and that changed my mind big time! I have built amps with El84s before, so I'm getting an idea of what they can do.

13

Just a little update on this thread. I found a neat little adapter that will allow you to use 6V6 tubes in an amp wired for 6973 power tubes that plugs right in without altering your amp in any way. I ordered 4 of them online and tried them out in my Magnatone 480 and they work great. If you have an amp where the power tubes are hanging upside down you might need retainers with these adaptors because they add weight but the cool thing is that they are very easy to plug and use without altering your amp in any way. They made my life a lot easier!

https://www.jukebox-revival...

14

That's some cool info Guitarcapo. Thanks!

Well the kit showed up today. A couple of disappointing aspects - the power transformer was not included - it is back-ordered. So i don't know when to expect that. Also, when they packed the chassis they used packing tape around it to hold all the parts bags inside the chassis. that's ok, but packing tape on metal surfaces is not a good thing. When you remove the tape all the sticky gunk stays on the metal, and in this case it is highly polished aluminium.

So i spent a good 15 minutes with a bottle of eucalyptus oil and a soft cloth removing tape gunk. It's all good now, but would have been easy to avoid.

I will try to take some pics tomorrow. I have some EH 6973s now and may as well try them. If they sound awful I will convert the amp to EL84s. The chassis seems well made and beautifully polished. I guess I have been spoilt a bit by choosing only my favourite bits for amps the past few years. I have to overcome my snobbishness in building a kit.

15

What's the deal with that phase inverter? I've never seen anything like it.

Edit: oops, looks like the elusive paraphase inverter, where the signal for the second triode is tapped off the output of the first plate. Thanks Merlin!

I love these wacky old PI circuits. I think they're really responsible for why a lot of these amps don't sound like the common Fenders, etc. of the day.

Also check out that trem circuit. It appears to have the same oscillator stage as most, but the oscillator is then fed through a cathode follower to the bias on the first signal tube. Cool stuff.

16

Hey Jimmy. How big is that Watts chassis?

17

Huge! 21.5" L x 5.5" W x 2.5" H. Not sure I have a cab which will fit it. Found another oddity today - I have no 35uF/50V caps - I need two for this amp. But they did supply two 100V/50V Spragues, which I need none of. Hmmm...

They also supplied four rubber grommets, all of which fall out of the chassis as soon as you place them in there because they are too small. And I have no idea what the secondary taps of the O/T are. From the layout drawing I think the black wire is common, but I have a green and a yellow for one output socket. I don't know what impedance they might be. I have connected the yellow to the output because that's what the layout shows.

Here is where I am at right now. I had to shoot at an angle because the chassis is so reflective.

18

It would have been nice if the kit had come with some basic documentation. There is not much to go on at the site either - there is a layout and a schematic, but no transformer diagrams.

So far I think the kit is of decent quality but needs more attention to detail. Or maybe I'm being my normal, overly anal self. I like things to be right.

19

Well I spent a few evenings comparing the sound of my Magnatone 480 with four 6v6 tubes and RCA 6973 tubes and I believe with my amp the 6V6 sound a tad better. A bit more clean bottom end and headroom. I'm using adapters so I can always go back but for now I'm keeping it this way with 6v6

20

Good to know. I'm slowly working through this amp, and have wired the first channel so far. But I emailed the people who make the kits and have not heard back yet - I still need the power tranny which didn't come with it.

21

O.k. I spent a little more time with my amp. The 6V6 sound a bit nicer but it's a really subtle thing that I could probably get with an EQ pedal to scoop the mids slightly and using the 6973 tubes. The 6V6 tubes are too large for me to use with the adapters and have the back panel on. They're kind of awkward so I decided to go back to the 6973 tubes for now. On a whim I tried the Electro Harmonix 6973 and I'm starting to think I was a bit too harsh in my assessment of them. I did some mods to the amp and now they sound pretty good in there so I think I'm going to use them.

I've always said that you can have more results swapping out a small cap or resistor inside an amp than all the tubes in the world and this was another case like that. I added a cathode cap and resistor to one of the preamp gain stages that was simply grounded and the amp came alive. It sounds great now and the 6973 tubes are doing o.k. Enough so that I'm happy with the amp's sound as it is and I'll probably use them as they are new, balanced and dealing with all of 400 volts on the plates. I'll save the NOS tubes instead of using them up.

22

Well that's good news! I've got the amp all together now except I'm still waiting on the power transformer and a couple of bypass caps. I'll post some pics soon. The layout is a bit weird - the first and third tubes share a cathode resistor so I have a wire going between those two tubes to link them. Never had to do that before.

Living in Australia it always takes longer to build an amp than it should, because it takes ages for the parts to get here.


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