Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: labb on August 28, 2024, 08:50:22 am

Title: Choke selection
Post by: labb on August 28, 2024, 08:50:22 am

Need some help on selecting a choke for an amp. Amp will be set up to use either 6v6 or EL34 power tubes. Voltage is 390 V. Three 12ax7, 2 EL34 or 2 6v6. I know that a hammon 156L works for the 6V6’s. Not sure about the EL34’s. Just never have learned how to size chokes. Thanks for any help.

Title: Re: Choke selection
Post by: mresistor on August 28, 2024, 09:49:10 am

Aiken has a good discussion on chokes. https://www.aikenamps.com/index.php/chokes-explained (https://www.aikenamps.com/index.php/chokes-explained)


in this discussion Merlin also talks about the choke and uses and example like you are wanting to build  https://valvewizard.co.uk/smoothing.html (https://valvewizard.co.uk/smoothing.html)


You are using a capacitive input power supply and probably using the choke to filter the voltage for the screens and down the line.  The requirements are not as stringent as for a choke input ps.
Probably any choke used for 6L6 or El34 amp would suffice. 

 The Fender Twin uses one rated for 90ma https://www.tubesandmore.com/products/choke-4h-90ma-fender-6l6-amps-125c1a-replacement (https://www.tubesandmore.com/products/choke-4h-90ma-fender-6l6-amps-125c1a-replacement)

Title: Re: Choke selection
Post by: tubeswell on August 28, 2024, 03:42:12 pm

The key constraint is peak current the choke will see.

A choke in a CLC filter between the OT/Reservoir cap and the rest of the amp (i.e. screens/smoothing cap onwards) only needs to supply enough current for the screens and the preamp tubes (including the PI). See the picture at the bottom of the page on this link https://www.valvewizard.co.uk/smoothing.html (https://www.valvewizard.co.uk/smoothing.html)


(Whereas a 'whole-of-supply' choke will need to supply the OT current as well)

Title: Re: Choke selection
Post by: mresistor on August 28, 2024, 04:02:07 pm

Thanks Tunbeswell   I thouoght of that when I got off the keyboard..   that's why that Twin Rev for instance only needs a 90ma choke.    So the one the OP recommended is probably fine too. 


I deleted what I had said as it was for total amp current - not from the screens and on.

Title: Re: Choke selection
Post by: labb on August 28, 2024, 06:33:45 pm

Thanks for the input. I chickened out on the choke. I will just go the big old resistor route. Try finding a 130 ohm 25 watt resistor. Had to resort to eBay.