5C1 transfomer heater elevation or center tap?

[plumcrazyfx]

Okay.  I'm scratch building a 5C1 and still need to pick a power transformer.  Would it be better to find one with a center tap for the heater or would elevating the heater give me a quieter amp.  I'm leaning toward elevating with a pair of 100ohms from the heater to the cathode resistor/bypass cap to ground (partially as a test).  I was looking at a Hammond 272BX (300/300) but I have heard the elevating requires you to have a bigger transformer than without.  Any help is appreciated.  Technical details about why would also help - I want to understand the how rather than just a yes/no.  Thanks.

[kagliostro]

You can go elevated with CT or with resistors (the better with a 500R pot)

High Voltage consumption increases, but only a bit

http://www.valvewizard.co.uk/heater.html

Franco

[plumcrazyfx]

Is one way better than the other?


Is the voltage consumption significant enough that you see an impact to plate voltage or need a bigger power transformer?

[John]

Is one way better than the other?


Is the voltage consumption significant enough that you see an impact to plate voltage or need a bigger power transformer?

No, your PT will be just fine either way. The humdinger is the "best" way, as it allows you to precisely balance the filaments. However, many times it's not needed. It is easy enough to do that I nearly always do it though. The balance pot can be any value between 100 and 500 ohms.


The 2 resistor method works fine too. And tons of amps just have the CT for the filaments too.

but I have heard the elevating requires you to have a bigger transformer than without.

I've never heard that. 

[plumcrazyfx]

I have a Bassman 20 that has the humdinger.  My space is very limited in this chassis (Hammond 1590S) so it would be a struggle to add it to this build but that would be ideal.

[kagliostro]

There are many places where you can put the pot inside a chassis

--

from Merlin's site

a 500 ohm pot will dissipate less than 80mW at 6.3V.

think to a 500R pot as 2 x 250R resistors, a pair of 220R (a value that is commonly used for this purpose) will dissipate a bit more

but it is a small current anyway

Franco

[sluckey]

My space is very limited in this chassis (Hammond 1590S) so it would be a struggle to add it to this build but that would be ideal.

Wow! That's a tiny chassis. Roughly 4" x 3" x 1.75". You may not even have space for two 100Ω resistors for the heater circuit. I'd just get a transformer with a center tap on the filament winding. Connect the center tap to the cathode if you want to elevate. This is quite a challenge. Please show us some pics.

[kagliostro]

  10cm x 7.6cm x 4.44cm  

I don't think you want to use octal tubes

Franco

[plumcrazyfx]

Oops.  Meant 1590R. Not quite as impressive.

[sluckey]

Oops.  Meant 1590R. Not quite as impressive.

That one is 7.6 x 4.4 x 2.4 inches. I'd still like to see some pics.

[plumcrazyfx]

I will try to figure out how to post some pics.  This is a second build trying to include some tweaks that I want to add this time around.  I don't want to use a power transformer with a large cutout like the first build so that's why the Hammond 272BX- no center tap so I need to figure out what I want to do (elevation, artificial center tap, or humdinger).

[kagliostro]

I will try to figure out how to post some pics.

Upload (it is free and didn't require registration) your images at http://imgur.com/

copy the link of the image, post here using the image TAG (the small icon with Mona Lisa that is under the Bold icon when you post)

Franco

[plumcrazyfx]

Here is a pic of the first go-round.  Wanted to tweak it - move some jacks a 1/4", use a different cap can, don't use a transformer with the large cutout, and redo the caps on the 6SJ7 so there is a bit more room.  Other than that it sounds good.  The Hammond for use without the large cutout doesn't have a CT on the heater - so I figure if I need an artificial I might go with elevation (or a humdinger based on some input here).  The purple wire and hanging CT was just a test at elevation.

[John]

Wow, that IS tight! Nice looking build though IMO. I was thinking about your artificial CT for the heaters. IF you can cram one more thing on your power tube socket, I think it would work to run a 100 ohm resistor from each filament pin to your cathode pin, i.e. 2&7, junction at 8.


If you do want a humdinger, I have some mil surplus (Russian I think) 200 ohm pots with a very small footprint, pot body is 3/4" at most. If you want I'll mail you one.