New 5C1 build design question.

[chikov]

A couple of months ago I was given an old Oscillograph from the 50's. I went through it and saved some parts and pots. I was happy to find 2 good 6SJ7 tubes in it. When I researched them, I found out that Fender used them in their Champ amps in the 50's. Naturally I decided to build one of those amps and practice using my new Oscilloscope
I decided to try to use a few good mods like cap totem pole stack near st by switch and adding back up diodes to the 5Y3 rectifier. The question I have is:
Why did Leo placed the 2 filtering caps (8uf) in parallel on the first and second node with 500 Ohm resistor in between in his power supply? If I will use say 100 uf + 100 uf totem pole caps, do I still need both of those 8 uf caps?
[IMG:640:529]http://i409.photobucket.com/albums/pp171/alexjohnne/champ_5c1_zpsa7bkjimq.png[/img]

[martin manning]

Single ended amps like the Champ benefit from some extra filtering before the plate node since the ripple voltage (hum) will not be cancelled in the power stage as it is in a push-pull amp. The extra R-C filter (500R-8uF) is there for that purpose. Later champs used a single 16uF reservoir, but that will still have a bit of hum. I wouldn't bother with a standby switch, and I would not put a large reservoir cap after the rectifier. To minimize the hum, I would keep the C-R-C, but replace the 8uF's with 22uF. If you want to make it really quiet, replace the 500R with a 4H 50mA choke as used in a Deluxe Reverb.

[chikov]

Thank you, Martin! I was going to ask about the choke next, but you are one step ahead of me - wow.

[chikov]

If you want to make it really quiet, replace the 500R with a 4H 50mA choke as used in a Deluxe Reverb.

Martin, I have two vintage chokes - one bigger in size but reads about 90 Ohms and the smaller one but it reads 1000 ohms. Which one should I use? How do you really measure them?

[martin manning]

I think I would try the one measuring 100R, unless you want to drop a lot of voltage. The current demand for a 6V6 and a 6SJ7 is pretty low, so I don't think there is much chance of overheating. A specialized measuring set up is required for power supply chokes since the inductance is quoted at rated current.

[Stevem]

One flaw in these amps is no screen resistor, so adding in even just a 250 ohm 2 watt resistor is a good idea!

Also do not wire it with one leg of the heater feed grounded to the chassis, run the normal two wire set up with a added 100 ohm 1/2 watt resistor from each heater leg to ground, that is unless the PT you will be using already had a center tap of its own.

[tubeswell]

THe advantage of HT chokes is that they have almost no DC resistance, but high AC impedance. Therefore, all other things being equal, the reason you want to use a HT choke because it won't drop too much HT voltage and it will provide near perfect ripple reduction.

But the voltage drop depends on the current being supplied, and if the current demand is not high, then the voltage drop won't be very significant either. Nevertheless, in a 5C1, you still have about 40mA current draw on the HT winding, so 1,000R x 0.04A = 40V drop. Whereas the 90R choke only loses 3.6V, which all other things being equal = a bit more signal headroom.

[TUBEDUDE]

Some small noise improvement may be had by tying your new heater center ,as given by Stevem, to the power tube cathode instead of ground.

[Kagliostro]

If you want you can save the money for the 5Y3 tube and use a PT with a bit less AC

Solid State rectifier is good on SE amp, they has not tendency to SAG, so the use of a vacuum tube rectifier can be avoided

BTW, if you want SAG on an SE amp, you can add a large resistor in series with G2 (try 2.7k as to begin then lower or elevate the value at your taste) a switch in parallel with this resistor will give you the possibility to exclude it when you don't want SAG

Franco

[rp]

https://tubeamparchive.com/viewtopic.ph ... hlight=5c1

Here's my 5C1 from a long while back but it might interest you. The way it's built turned out dead quiet, can't even tell it's on, but it's also a low power, low gain amp which has something to do with that, but still no hum even w/ a 12". It's a great little circuit, my tips:

Use the 5F1 power string, no reason not too, the 5C1 string didn't suggest any particular vintage mojo to me and I wanted to use it with speakers bigger than a 6” or 8” so I changed it. But keep the caps pretty low in Champs, I found the looseness helps them sound fatter, it's one of the differences btwn the tweeds and the BFs. I see no point for choke, though I never tried it. I recall a Gerald Weber tweed Champ article saying it brings no goodness. I’ve built several Champs, never any hum problems.

Keep the grid leak input, at least try it out. It's very cool, has that touch sensitive clean to mean as you dig in, even though it's only for a few watts of bite. You can always try cathode bias with a few minutes of work. If you intend to use pedals grid leak won’t do, but one builds a Champ exactly to avoid pedals - it is a distortion pedal.

Use good iron. Allen or Heyboer will make it sound Fendery, Edcor will make it sound real good but not Fendery.

Think about upping the PT by maybe 25V. Mine came out at about 300V, as is correct, but imo it could use an extra watt or two, maybe try for ~360V, unless you really want only a bedroom amp.

I added to mine a pretty cool preamp option, simple line out w/ a load, works well as a PA preamp, I was hoping for a wild tube overdrive feeding an other amp but it actually keeps its modest 5C1 character out the line on the resistor load.

[Roe]

I like the 5e1 power supply with an extra node for the screens. I'm using 22uf, 10uf, 10uf, 10uf

[chikov]

Thank you, gentelmen, for all your huge help. I am sorry for the delay in posting any updates - life and work got too busy. And yet, in the middle of all this business I was able to get some missing parts from Weber Speakers and finish my little amp. I used three vintage tube sockets, vintage choke and 6SJ7 tube, the rest is from Weber. The chassy does not look super neat like most of your ones but it works. I do not hear much noise - that is good. Here is a couple of photos:

[IMG:640:480]http://i409.photobucket.com/albums/pp171/alexjohnne/4693E4F4-9748-4AC1-A818-45469EDA9025_zpslhtinbbh.jpg[/img]

[IMG:640:480]http://i409.photobucket.com/albums/pp171/alexjohnne/BA542256-3B43-4DC3-AF6C-51BEDBAC9948_zpszinxojrk.jpg[/img]

[IMG:640:480]http://i409.photobucket.com/albums/pp171/alexjohnne/0193824D-F2A6-4C4D-A2E2-ACCDD910AB2E_zpsuk4zoh1d.jpg[/img]

One complaint - it is too quet.. some one said that their's has a plenty of overdrive, but mine is very clean even when the volume pot is all the way up. It sounds better with my modded Boss Dual Overdrive, but I wonder if i can make it dirtier and louder without pedals?
I will re reed all you suggestions again, i might try to raise the plate voltage from 300 To 330 ( my PT has that option)... thank you again and Happy Thanksgiving to you all!

[tubeswell]

A 5C1 is what it is. The design goal at the time was to build a simple amp that was as clean as could be achieved with as few parts as possible for students to practice on.

[JazzGuitarGimp]

So, what's the little peep hole on the chassis just behind the power switch? It looks interesting and intriguing....

[chikov]

So, what's the little peep hole on the chassis just behind the power switch? It looks interesting and intriguing....

The amp chassis I am using came from a cheap Raven amp (I bought it broken at the Pawn shop for $10.00). So, when it goes inside its cabinet it uses 2 extra tabs to secure itself to the front wall. they just cut and bent 2 tabs away from the bottom of the chassis and left the two peep holes
PS you can see them better on the last photo.