New 80 Watt Wreck done!

[M Fowler]

Anyone else besides me building one of these 80 watt Express? Finished up the main board and built the bias board but had to order some 180K resistors to finish it. I had delayed my mouser order and now here I sit. Faceplates shipped and will arrive next week. PT/OT are being wound as we speak by Edcor.

Using 20x8x2.5 turretboards.com chassis
Express board turretboards.com
Cap/bias board material turretboards.com
Edcor XPWR108 PT 300-0-300 250Ma/6.3v 4A (hope that is enough power)
Edcor CXPP100-MS-4.2K OT 4,8,16
Bias points from Hoffman
Alpha pots Mouser
DPST switches 103-0016-EVX Mouser
Bourns 10 turn pot 20k

Give me some feed back on that power supply as I think I should be sitting somewhere in the 350-400Ma shouldn't I rather than 250Ma.

[Shermock]

Hello Mr. Fowler

I think, off the top of my head , that an EL34 wants 1.5A heater current each. So figure 6A heater current for just the power section, and another amp for the 3 preamp tubes (300mA each, I think). So the heater supply needs to be pretty beefy--7 amps at least.

Your idea for 350-400 mA on the high voltage supply seems right on to me...

Anyway, that's all I know in a nutshell...for tonight, at least...

Shermock

[M Fowler]

Oh your loads of fun now I have to order a larger power supply

I thought about it when I ordered the other one but then ordered anyway as I can use it for another build.

Alright I will sit down and calculate it like I should have in the first place.

Thanks Shermock

Anyone else want to pick on me or have tranny advise?

Mark

[breakfastbuddy]

but you need more filament current for the pre amp . since 4 a goes to the power amp section , unless you use 6l6 tubes . you can use a separate 12,6 volt for the preamp at .45a

[paulster]

The standard Toneslut tranny is 300-0-300 at 300mA with 7.5A on the 6.3V supply. You need 6.9A for the heaters and 300mA might just about be enough for the high voltage supply.

By way of comparison a Marshall 100W tranny is about 475mA on the HT supply.

I can't remember if Allyn posted the specs of what he used, but the Edcor with 250mA seems way too low, and the 4A heaters means you can't run a quad of EL34s even without the preamp tubes.

[John_P_WI]

Hi Mark,

Excuse me for not reading the whole thread, but looking at your specs above:

Back of the envelope calcs:

Some EL34's pull upwards of 1.8 amps. Therefore 1.8 a x 4 is 7.2 amps alone of the EL34's. Don't forget to add the 12a_7's. I would spec 8.5 amps total. That'll give about .4 amps safety IF you use some thirsty EL 34's or other.

The pt at 300 - 0 - 300 will give around 425v. You will need just under 400 ma to get the 80 watts.

I do question the ability to get 80 watts out of the 4.2 K OT listed. Seems a little high to me....

Sounds fun and good luck,

John

[Allynmey]

The trannys are under powered listed here. The customs I used were about 450mA+ with 10 amp filaments. The OT was 3.3K primaries.

[M Fowler]

Thanks guys I will see if I can fine a suitable PT as the OT is a 100w tranny and should work.

Mark

[Structo]

WOW!

That is a huge PT!

I hope you can find something that will work without a custom wind.

Mark, it looks like you have a few irons in the fire, eh?

Can't wait to see this one completed.

[M Fowler]

I was looking at the Marshall replacements but the sites did not publish the specs so I was unsure of the correct mA rating I needed. Also forgot I had to increase the filament supply amperage.

I haven't seen anywhere that Allynmey's 3.3k primary OT for 80 watts so his must be custom OT as well.

Usually 4 EL34 or 4 6L6 run 1700 to 2200 ohm pimary OT I figured but then saw that Edcore noted the 100 watt OT at 4.2k closer to what Allynmey was using.

I sent Edcore a message to see if they started on my production run yet as it takes 4 weeks lead time.

Mark

[guitardude57]

Hi guys,

I really want to build this 80 watter. Is there a current rev of the layout and BOM, and Schemo for this? I found one earlier one, don't know if it is a final version. Also thinking of a half power switch to cut two of the El's off when wanted. Any word on the Edcor trannies? I am pretty excited about this build. Sounds like a perfect project, as well as a flexible, monster tone amp. Now maybe the SLO 100 could be the back up amp for a change! Thanx, Mike

[M Fowler]

guitardude57

The layout posted is the final version.

Both you and I will probably have to do some home work to fine a suitable PT and OT or run four 6L6s tubes with high power fender tranny set.

Or run four EL34s with Marshall set.

Another option is to contact Heyboer or Edcor and have special wound sets made. Unless someone else has suggestions.

Allyn if I talk with Heyboer can I ask for for your line card on this?

Mark

[Allynmey]

These were customs from Pacific. Started with Ken's line card and adjusted accordingly.

[M Fowler]

I once again went through the various suppliers for ideas on trannies and this is the list I find, some specs are not available but it doesn't show that I require 10a filament supply?

Edited:

It looks like 6A for the four EL34s and 12AX7 = 3mA each .3. equals 7amps and 7.5 to 8 to be safe. To push it harder and allow for some tubes that go higher then 10A is about right.

Mark

[M Fowler]

DR103 Hiwatt calls for PT 340-0-340, 500ma. 6.3v 7A four EL34s
OT 2000 ohm center tapped for 100w rating.

Twin Reverb PT 340-0-340 450ma 6.3v 7A four 6L6s
OT 2000 ohm 100w rating

So all this has me confused.