rob@tele wrote:According to the layout of the 183, the power transformer is a replacement for a fender twin. As 183 has EL34's I guess that it is not a problem for the power transformer to handle the extra 0.7x4 = 2.8 A (6L6 0.9A v.s. EL34 1.6A) heater current. Am i right?
You are close
However, A Twin has a 6 x ecc83/81, therefore the calculation is
Twin (6L6 0.9A x 4 + 0.3 x 6 =) 5.4 A
#183 TKT (EL34 1.5A x 4 + 0.3 x 3 =) 6.9 A
Difference: 1.5 A
Twin transformer (290FEX/ 125P34A / 022756) is nominated for 6.5A.
The #183 consumption is 6.9A - so an extra 0.4A (6%) is no problem.
Fender must not have cared either, the twin had 3 extra preamp tubes. Adding another .9 amps of current requirement. If you read the published specs on most twin replacement trannies you will find that they are unpowered on the filaments. Zero headroom
According to most I've talked with in the transformer industry most of popular names mention here rate their transformers conservatively sometimes as much as 35% being around the industry standard for a well built hefty power transformer (Twin/ Bassman replacement) from Hammond or Mercury Mag or Heybour..Not the cheap China stuff..In some and most cases you can meet and even slightly exceed the power rating and still be OK.. Obviously manufactures like myself like to stay within the rating of the PT for liable and warranty reasons but since this is a do it yourself forum use your best judgement..
Tony
" The psychics on my bench is the same as Dumble'"
talbany wrote:According to most I've talked with in the transformer industry most of popular names mention here rate their transformers conservatively sometimes as much as 35% being around the industry standard for a well built hefty power transformer (Twin/ Bassman replacement) from Hammond or Mercury Mag or Heybour..Not the cheap China stuff..In some and most cases you can meet and even slightly exceed the power rating and still be OK.. Obviously manufactures like myself like to stay within the rating of the PT for liable and warranty reasons but since this is a do it yourself forum use your best judgement..
Tony
I agree, I typically spec my transformers with 25 to 50% headroom for reliability. Power trannys always M6 iron.
Located in the St Croix River Valley- Afton, MN
About 5 miles south of I-94
aka K0GWA, K0 Glas Werks Amplification www.glaswerks.com
I talked to Patrick at Mercury Magnetics, He said their Twin replacement PT (FBFTP) would be Ok for running 4 El34's. He said the PT may run a little warmer, but it would be fine.
Don't forget that the heater current is generating about 6.3*1.6*4=40 W of heat (with 6L6 you get 23W ). Add to that the dissipation of the tube itself, lets say 4*10=40W () and you have 80W of heat dissipation. With an upside-down chassis, this will heat-up the chassis quite well.
And the last time I touched a working light bulb of 80 Watts, I burnt my fingers....
Nice..No doubt fans are great..Even if it's a small 12v cheap computer fan..Just to keep the air moving..Other things that help w/ transformer heat are
X-Mount (or in chassis mount) transformers since the chassis acts as a kind of heat sink..
Opt for a transformer that doesn't use a full wave bridge
Try not to use one that's not designed to use w/FWB
Tube proximity..Keep em at least an inch away
Thought I'd mention..
Tony
" The psychics on my bench is the same as Dumble'"
