pt sourcing

[Bugman3183]

hello all,  I'm interested in building a 18 watt tmb ef86 which has 2 el84's 3 12ax7's and one ef86.  trying to find a suitable pt for this project and was looking at the classictone 18 watt model.  It is rated at 290-0-290 @ 120ma 5v@ 2a and 6.3v@ 3a and wanted to know if this would work.  Also if there an equation for figuring this out that anyone could share with me so that I won't have to ask the same question for my next project would be greatly appreciated.  Thanks.

[tubenit]

You could consider Hoffman's 18w PT and/or OT.  He carries excellent products and the shipping is incredibly fast!


With respect, Tubenit

[sluckey]

That PT will work fine. Hoffman also has a fine set of iron for the 18 watters.

[Bugman3183]

Cool,  thanks guys.  When I looked at the hoffman set I didn't see any info on the rating for it.  But if it'll work, that's definitely the route I'll take. I appreciate the help.

[sluckey]

I built a standard 18 watt amp using Hoffman's iron. B+ right on the rectifier output was 342vdc. Filaments are more than ample. And you have a choice of 6.3 or 5 vac for rectifier filament.

[John]

I also use Doug's 18W set. For the EL84s, you might find you need a NOS 5Y3 to get the plate voltage around 350 or so.

[kagliostro]

To have an approximate idea of the PT you need for your further build

http://www.dreamtone.org/Calculate_Current_Form.htm

K

[Bugman3183]

Thanks for the link, should come in very handy.  When I used the calculator it said that I would need 3.8 amps for the filament winding.  So does this mean I need to get a pt with a minimum of 4 amps on the filament winding?  I feel like this is a stupid question, but I'm just not sure if there's any rifle room there.

[Bugman3183]

Ok, so I just ran the calculator again but using a5y3 as opposed to the ez81 and the results were 2.8 amps on the filament so that should be fine.  Thanks for the advice.

[kagliostro]

For filament the question may be solved simply looking to the tube requirement and sum the requirement of all tubes (must look to the required heater voltage 5v - 6.3v - 12.6v ........)

use this search engine for tube datasheet

http://tdsl.duncanamps.com/tubesearch.php

K

[HotBluePlates]

When I looked at the hoffman set I didn't see any info on the rating for it.

The relevant Hoffman ordering page has a link to the specs in the Library of Information.

Granted, Hoffman's info doesn't provide the current ratings, but he does say it's a Heyboer 18w transformer. Had to do some searching, but probable complete specs are here. The upper "Heyboer" diagram matches the details Hoffman does include on the site.

[John]

Well since we're talking about the 18W trannies from Doug, if I popped in 5881s (in place of 6V6s) would I risk frying anything at full roar? I tried some Tung-sol RI a while back without *really* pushing things and liked the sound.

 I  know they draw more current, but sometimes just asking you guys is easier than calculating from data sheets that might not tell the whole story.

[Bugman3183]

Thanks hbp,  I must have overlooked that somehow.

[EL34]

When I looked at the hoffman set I didn't see any info on the rating for it

There are links to the tranny specs pages on my transformer page and on the library page

http://www.el34world.com/Transformers/marshall.htm