Help Building a Champ??

[Jaicen]

Hi guys, i'm looking for a little help. I used to frequent this place quite often, but it's had a bit of a facelift since I was last here

Basically, I want to build a champ clone (5F1), but I need a little help with the power transformer. I'm in the UK, so sourcing parts seems a little harder than in the US, but I think I have something.
If I were to use silicon diodes to rectify the power supply could I use a transformer with 240 - 0 - 240 secondaries? Or would that push my voltages up too much?? The one i'm looking at is: HERE
It's attractive, because it's cheap and accessible. I can't find anywhere that stocks the hammond PT's.
Are there any places in the UK I could look to for alternatives if this is no good??

[steve]

That looks like it would work fine. You'd get around 300-310v which works well for Champ circuits. The secondary is rated for 150mA, which is overkill for a Champ, but it would work.

steve

Hi guys, i'm looking for a little help. I used to frequent this place quite often, but it's had a bit of a facelift since I was last here

Basically, I want to build a champ clone (5F1), but I need a little help with the power transformer. I'm in the UK, so sourcing parts seems a little harder than in the US, but I think I have something.
If I were to use silicon diodes to rectify the power supply could I use a transformer with 240 - 0 - 240 secondaries? Or would that push my voltages up too much?? The one i'm looking at is: HERE
It's attractive, because it's cheap and accessible. I can't find anywhere that stocks the hammond PT's.
Are there any places in the UK I could look to for alternatives if this is no good??

[Jaicen]

Overkill is good At that price I'm sure it will be fine.
This is my first amp so I don't want to go crazy buying NOS everything till i've ironed out the wrinkles.
When you say that it will output 300--310v, is that with silicon rectification or a rectifier tube?? How do I go about finding the voltages I need, and working out what the PT will give me? I'm feeding it 240V on the primary by the way, so would I use both ends of the primary??

[MWJB]

Usually a full wave SS rectifier will give you 1.4 x B+ secondary voltage, therefore 240x1.4 = 336v...less a little depending on load. This is a little on the low side for a 5F1 champ, but will work.

Yes, you would use both ends of the Primary and tie them in series (connect 115v tap of the 1st winding to the 0v tap of the second winding). That'll set you up for 230v, it might push up heater voltages slightly but so long as you end up at 6.9VAC or under I wouldn't worry.

You do know that TAD in Germany carry a good range of repro trannies, chassies & parts, delivery to the UK is usually around a week? The 5F1 PT is E110 plus shipping (around £90-ish to the door?).

Bluebell Audio in Dundee carry the Hammond transformer range as well as many useful parts for your project.

[Colin]

Hi Jaicen

I don't wish to be a smart-arse or anything, but the UK mains voltage was changed to 230V quite a few years back now to fit in with the EU voltages. This will only change your calculations a bit, but it's worth knowing.

Colin

[MWJB]

YMMV but 230 is usually the lowest voltage that I see from the wall, it averages more than that, but you're right it is only a few percent difference at the end of the day. The unknown quantity is how accurate the transformer specs are, so still check your heater voltage. A few more volts on the B+ secondary would be no bad thing.

[MWJB]

In fact, I just remembered that I used a 254-0-254VAC rated PT in a build recently and that only gave me 310vdc after a SS rectifier. So personally wouldn't go for the Maplin PT. Check out Bluebell and see if they have a Hammond with a 300-0-300, or slightly higher, secondary. You'll probably get a valve rectifier option too.

[Jaicen]

That is interesting actually, when exactly did we switch over?? I'm surprised I didn't hear about it to be honest, it's something I think I would have expected to pick up on.
From what i've read, 310v seems to be right in the voltage range for a Champ, or am I missing something??? If so, could you direct me to blubell? I assume it a shop, but i've not been able to google anything.

[Satamax]

http://www.tubetown.de/ttstore/produ...att-Style.html

[MWJB]

310v is a bit low for a 5F1 champ, the schematic shows 340v allow 10% rise over that for escalating wall voltages and you get 370-ish. But these things aren't written in stone, there's no reason why you couldn't build a 5F1 circuit running the lower voltages...but I wouldn't. You're not going to have a lot of headroom, so I'd prefer more B+.

www.bluebellaudio.com, 01382 322990.

[steve]

In fact, I just remembered that I used a 254-0-254VAC rated PT in a build recently and that only gave me 310vdc after a SS rectifier. So personally wouldn't go for the Maplin PT. Check out Bluebell and see if they have a Hammond with a 300-0-300, or slightly higher, secondary. You'll probably get a valve rectifier option too.

The Maplin PT will be fine.

Why would he want to use a valve rectifier? The Champ is a Class A amp. With near constant current draw on the power supply, a tube recto won't sag. Sag is great for an Class AB amp, but doesn't really occur in Class A.

A tube recto will drop the voltage due to internal resistance, but as the PT's voltage is on the low side, he doesn't need to drop the voltage any.

I've built lots of Champs/Tweed Princeton style circuits using SS rectifiers and 240-0-240 rated PTs. 6V6s sound great at about 300-310v. No worries there.

As far as headroom goes, the 5F1 champ is a 5 watt amp. It is not a high headroom kind of circuit. It starts to overdrive early on and just gets crunchier and crunchier from there.

I've owned Silver Face champs, the ones that have 400v on the anode. They sound shrill and sterile to me. They also run the 6V6 tube too hot. Granted NOS tubes can take it and many have lasted decades in Champs, but I'm not so sure about current production tubes.

steve

[Colin]

If you're really interested in the UK mains supply then read on....

The United Kingdom for many years had a standardised supply voltage of 240V ±6% (415V for three-phase) whereas continental Europe had a nominal supply level of 220V (380V). From 1 January 1995 the nominal voltage across Europe has been 'harmonised' at 230V/400V.


This is not a real change, since the former 240V countries, including the UK, have in the first stage of voltage harmonisation a tolerance of 230V -6% to +10% (i.e. 216.2 - 253V) as compared with the 'old' limits of 240V ±6% (i.e. 225.6 - 254.4V). However, the former 220V countries (most of Continental Europe) have limits of 230V -10% to +6% (207 - 243.8V).


The Electricity Safety, Quality and Continuity Regulations 2002, which came into force on the 31st January 2003, replacing The Electricity Supply Regulations 1998, formally confirm the UK standardised supply voltage tolerances at 230V -6% to +10%.


Plans to harmonise the whole of Europe to 230V ±10% (i.e. 207 - 253V), which were due to be applied from 1st January 2003, have been postponed until 2008 at the earliest.


Phew!..now you know..

Colin

[MWJB]

"sounds great" is subjective, I never said it wouldn't work, or that Jaicen couldn't do it...just that I wouldn't.

The envelope of the note will change with different rectifiers, the voltage typically won't drop a huge amount because of the relatively small current draw in a Champ. The amp will not sound the same when you change rectifiers.

The original title of this thread was "help building a champ", whilst there are margins of tolerance, champs don't run 310v, or have SS rectifiers, though a sounding SE 6V6 amps might.

[steve]

The envelope of the note will change with different rectifiers, the voltage typically won't drop a huge amount because of the relatively small current draw in a Champ. The amp will not sound the same when you change rectifiers.

Could anyone pick out which was which in a double blind test? I doubt it.

The original title of this thread was "help building a champ", whilst there are margins of tolerance, champs don't run 310v, or have SS rectifiers, though a sounding SE 6V6 amps might.[/QUOTE]

The original questions were:

If I were to use silicon diodes to rectify the power supply could I use a transformer with 240 - 0 - 240 secondaries? Or would that push my voltages up too much??

The answer is yes, he could use that Maplin PT and no, it wouldn't push his voltages up too much. The voltages would be lower than a real 5F1 Champ.

Sounds like he isn't much concerned with an exact clone to me.

steve

[MWJB]

Oh, what fun...let's drag this splitting hairs out some more until we, and everyone else, are sick of this thread...

I CAN tell the difference, you can probably tell the difference. I can't believe that you are actually suggesting that there is no audible difference between a tube and SS rectifiers. That is astonishing to me.

Obviously, by Jaicen's further request for advice as to how to determine final B+ voltage, he wasn't sure what he was going to get, whether shooting for "clone" voltages or not.

Jaicen if you want to use that Maplin PT please do, it will work and may sound fine. Steve has used similarly rated PTs (I have too in the past) and says it sounds great, I don't disbelieve him. But if I was building a champ I'd go for a little more voltage and a PT that will accomodate a tube rectifier...then you could see for yourself what sounds like what, and what differences you could perceive. You might prefer a SS rectifier at the end of the day but then you would have the choice.