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5F1 Amp Kit

Mattyboy75

Member
Joined
Nov 15, 2020
Messages
79
Hi all,

looking to build a champ amp. Never built one before but I am a handy person and fine with a soldering iron.
any ideas for the best one? Im looking for the whole lot with cabinet and speaker etc.
I’m in the UK so postage and 110v may be an issue with US kits.
I hear the Tube Amp Doctor is quite good (Germany but only around £16 postage).
thoughts and opinions please.
 

jrgtr42

Well-known member
Joined
Mar 24, 2005
Messages
2,094
I don't know what shipping comes to, but I've been looking at kits on and off, amd many of the big companies have options for 220v power.
|I don't have any opinions as to which are best, though I;ve heard good things about Mojotone, Weber, and Mission, to start with. (over here in the States, at least)
 

PaulD

Active member
Joined
Jun 25, 2007
Messages
578
Last edited:

Mattyboy75

Member
Joined
Nov 15, 2020
Messages
79
Thanks Paul.
I have looked at theirs (they aren’t great at answering the phone though for questions)! I will probably go with them depending on the lead time for the cabinet if he answers my email.
I don't know what shipping comes to, but I've been looking at kits on and off, amd many of the big companies have options for 220v power.
|I don't have any opinions as to which are best, though I;ve heard good things about Mojotone, Weber, and Mission, to start with. (over here in the States, at least)
Thanks, I’ll take a look at them.
 

PaulD

Active member
Joined
Jun 25, 2007
Messages
578
Ah OK, it's a couple of years since I bought anything from him but always found him fine to deal with so hopefully things haven't changed? I know he is a one man business so maybe it is just that he is busy. He used to get the cabs from a guy called Chris in Kings Lynn, again a one man business, and typical lead times were around 3 weeks. They were very well made cabs. Let us know how you get on.
 
Last edited:

Brian H

Member
Joined
Dec 19, 2002
Messages
716
Mojotone has various voltage wiring options though shipping might be expensive. Great kits, though. I built a 5F1 last year and love it. Use stewmac directions to build from their website. Jupiter speaker and some old glass also help the tone.
 

mojodelic

New member
Joined
Jun 20, 2021
Messages
11
Like Brian H above I built a mojotone 5F1 kit using theirs and Stewmac's instructions. Very pleased with the results.
 

Mattyboy75

Member
Joined
Nov 15, 2020
Messages
79
Thanks for all the info guys. I have bought one from Modulus amplification here in the uk.
I have a question if anyone can help?
I haven’t plugged it in yet as I only finished it this morning but when doing a few checks, the green wires from the transfer to the lamp and on the the valves have continuity to ground on both sides of the lamp.
I have checked my wiring and there is nothing touching that shouldn’t be. Also the speaker Jack has continuity to ground on both tags. Is this normal when unplugged?
 

PaulD

Active member
Joined
Jun 25, 2007
Messages
578
That's perfectly normal, the heater winding of the transformer doesn't have many turns and hence will have a low DC resistance, the centre tap of the winding is connected to ground so you will read continuity through the winding. Same applies to the speaker jack, you are reading continuity through the transformer winding.
 

Mattyboy75

Member
Joined
Nov 15, 2020
Messages
79
Phew. Thanks for the info. Have to admit I had visions of unsoldering an awful
Lot of wires! Relief!
 

DutchRay

Active member
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Mar 15, 2015
Messages
354
Years ago, I had a bunch of tweed champs in the shop, '56, '58, 2x '59 and a '61, every one sounded great but they all sounded very different from each other. I wanted to build one and I got myself a modern champion 600 to gut and rebuild. I never did the upgrade since the champion 600 sounds pretty good and does everything I need it to do. Who knows, maybe I'll order parts and rebuild it in the future.
 

Mattyboy75

Member
Joined
Nov 15, 2020
Messages
79
Years ago, I had a bunch of tweed champs in the shop, '56, '58, 2x '59 and a '61, every one sounded great but they all sounded very different from each other. I wanted to build one and I got myself a modern champion 600 to gut and rebuild. I never did the upgrade since the champion 600 sounds pretty good and does everything I need it to do. Who knows, maybe I'll order parts and rebuild it in the future.
You should. It was a lot of fun to build it.
 

Mattyboy75

Member
Joined
Nov 15, 2020
Messages
79
Ah OK, it's a couple of years since I bought anything from him but always found him fine to deal with so hopefully things haven't changed? I know he is a one man business so maybe it is just that he is busy. He used to get the cabs from a guy called Chris in Kings Lynn, again a one man business, and typical lead times were around 3 weeks. They were very well made cabs. Let us know how you get on.
Hi, yes I did get hold of them and they were very helpful. Amp kit came in a few days. He has said the cabinet will be around 4 weeks but did say they are worth the wait. So I’m waiting! Thanks again for the info below on the transformer wires. I thought that might be a possibility but didn’t know for sure and didn’t want to have it go up in smoke! I was most worried about the speaker Jack to be honest as that is connected to the eyelet board and I’m not great with Schematics.
 

PaulD

Active member
Joined
Jun 25, 2007
Messages
578
Glad to hear all went OK with Modulus. The connection from the speaker jack to the circuit board is the negative feedback loop, a small part of the output signal is fed back to an earlier stage of the amp (the cathode of the second preamp stage in the case of the 5F1). The sleeve side of the output jack is grounded by way of the jack socket being bolted to the chassis which is why you get continuity between the tip and ground through the transformer.

This is a good site with lots of info about how valve amps work and how to follow schematics, it's well worth a read if you want to learn a bit more about the subject. https://robrobinette.com/Amp_Stuff.htm
 

Mattyboy75

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Joined
Nov 15, 2020
Messages
79
Thanks. Maybe you can help again! I have used a stewmac guide to plugging in for the first time. No valves all good. 5y3 and all voltages good. 12ax7 likewise. Plugged in the speaker and the 6v6 and after a few seconds it squeals very loudly. The speaker is not in a cab yet. I believe it’s oscillating. The tubes are all new straight from the box. Any ideas where to go next?
many help appreciated.
 

PaulD

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Joined
Jun 25, 2007
Messages
578
Yes, try swapping the 2 output transformer primary wires over, one wire goes to pin 8 of the 5Y3, the other goes to pin 3 of the 6V6, just swap them over and that will likely solve the problem.
 

Mattyboy75

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Joined
Nov 15, 2020
Messages
79
Yes, try swapping the 2 output transformer primary wires over, one wire goes to pin 8 of the 5Y3, the other goes to pin 3 of the 6V6, just swap them over and that will likely solve the problem.
Thank you. I’ll give that try.
 

Mattyboy75

Member
Joined
Nov 15, 2020
Messages
79
Before I do that, all the wiring diagrams show the blue wire going to the 6v6 and red to the 5y3. Are they not polarity specific? I have no doubt you have a huge amount of knowledge of these things but I just want to make sure.
 

PaulD

Active member
Joined
Jun 25, 2007
Messages
578
It's perfectly OK to swap them they are just 2 ends of a coil of wire in the transformer. The negative feedback I mentioned earlier has to be out of phase with the stage it is feeding back to, if it is in phase it becomes positive feedback and causes the squealing. It's quite common for this to happen on a new build and swapping the output primaries round will rectify the problem. Just to reassure you, yes I do know what I am saying is correct and safe to do, I build valve amplifiers for a living :)
 

Mattyboy75

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Joined
Nov 15, 2020
Messages
79
It's perfectly OK to swap them they are just 2 ends of a coil of wire in the transformer. The negative feedback I mentioned earlier has to be out of phase with the stage it is feeding back to, if it is in phase it becomes positive feedback and causes the squealing. It's quite common for this to happen on a new build and swapping the output primaries round will rectify the problem. Just to reassure you, yes I do know what I am saying is correct and safe to do, I build valve amplifiers for a living :)
Thanks again. I never doubted you knew what you were talking about but I would have been taking the word of someone I’ve never met before on what may have been a serious issue. I really do appreciate the help and I’m rather jealous of your job as I have enjoyed building my first one.
 
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