Specing a power transformer

[Dmoney]

I always have a spot of bother doing this...

I intend to do a project in a few months (aside from what im doing now) and I feel like having the option to run KT88's in it.

it'll be 4xKT88 with 5x12AX7.
I know the circuit of what im building will need to be tweaked. 100K grid to bias resistors, Bigger screen grid resistors. 1K/5W maybe 1K5. (nothing that will stop me using EL34's or 6L6GC's)

http://www.tube-town.net/ttstore/product_info.php/info/p5015_IGPW-Soldano--SLO100-Watt-Powertransformer.html

This transformer should give me a fair bit of B+ Voltage (im not after crazy watts, I just want to be able to drop in KT88s if i choose), and there is plenty of filament current available, more so than the hammonds ive been looking at... I'm just wonder about the current drawn on the B+ from the KT88's and 12AX7's.

I'll be full wave rectifying the B+. Probably get about 495v to the plate going off what is normally in an SLO.
(im not building a KT88 slo). KT88's would idle around 45mA I guess, maybe a bit more.

Is that trannie gonna have enough power?

[HTH AMPS]

Its a 0-360v HT winding, so you're looking at 500v rectified (before losses), probably 480v in the real world.

The specs say the HT winding is spec'd for 400mA, so I'd think you'll be fine with KT88s on that.  

You'll find that KT88s will idle at more like 60mA per valve at the voltages you're running, so even at idle you're looking at 240mA for a 100w amp.  Just run it with two KT88s and save some cash (and let your PT have an easy life).

Technical Data
Power: 366 VA
Primary: 0-230-240 V
Sec. 1: 360-0-50-360 V @ 0,4 A
Sec. 2: 6,3 V @ 9 A
Sec. 3: 6,3 V @ 2 A

[HTH AMPS]

btw, it looks like I'm getting a 100w Jet City head soon - do you have any experience with the IGPW SLO100 OT's as replacements in the Jet City amps?  http://www.tube-town.net/ttstore/product_info.php/info/p5014_IGPW-Soldano--SLO100-Watt-Outputtransformer.html

I'm assuming the mids especially will be sweeter - they always are in nicer iron as compared to the Chinese stuff, must be the metal used in the laminations.

[Transcend]

btw, it looks like I'm getting a 100w Jet City head soon - do you have any experience with the IGPW SLO100 OT's as replacements in the Jet City amps?  http://www.tube-town.net/ttstore/product_info.php/info/p5014_IGPW-Soldano--SLO100-Watt-Outputtransformer.html

I'm assuming the mids especially will be sweeter - they always are in nicer iron as compared to the Chinese stuff, must be the metal used in the laminations.

I dont have any personal experience but i plan on soon. Are you getting Adams? im surprised that thing has been lingering around so long at the price!

One thing to do is add the depth mod in too its a great little extra tonal shaping tool but im pretty sure you already knew that!

The general word on the IG trannies is that they are fantastic especially for the price. Also you'll get to find out what all the fuss is about Hi Def OT's now as theyre meant to be pretty much exact clones of the Deyoung SLO trannies or at least thats the impression the guy at IGP gives and has shown me several videos/photos of him deconstructing the deyoungs and taking measurements so it looks very promising.

[Dmoney]

one thing i haven't got my head around is HT current ratings and working out what I'd need for a given amp.
working out filament current needs is easy!

I haven't used the IG's but they look legit. I want to use them in an soldano related a build. not an SLO though. If the OT is a good copy of the Deyoung then id be happy.

[HTH AMPS]

AX84 has a great FAQs section, very useful.  Here's the one on specing PTs...

http://www.ax84.com/faq.html#PT-cur-req

Yep, its Adam's amp and yes I'll be doing the depth mod - I put it on everything these days, it just gives SO much balls if you are unable to really crank the amp.

The IG transformers are the same company that used to be Shinrock - I've had custom stuff made off him before, very well made iron and he will do custom stuff (one offs) at reasonable prices.  I've still got an 18w OT he made for me but used a bigger core so I could max the amp and not have the OT compress into oblivion.  Also had a choke made to run in a Sound City L120.

[JacksonRR]

Depth mod..... :?
You boys talking about a resonance circuit or what?

[Transcend]

Depth mod..... :?
You boys talking about a resonance circuit or what?

I think so its for variable negative feedback in the power amp

[Dmoney]

yes. same thing... well... sometimes its the same. haha... unless you're getting jazzy and using an inductor in it.

[JacksonRR]

yes. same thing... well... sometimes its the same. haha... unless you're getting jazzy and using an inductor in it.

Oh man... I'm trying hard to remember who uses an inductor in their resonance control.... Is it Mesa?

[Dmoney]

yes. same thing... well... sometimes its the same. haha... unless you're getting jazzy and using an inductor in it.

Oh man... I'm trying hard to remember who uses an inductor in their resonance control.... Is it Mesa?

the main one i know is bogner

[HTH AMPS]

yes. same thing... well... sometimes its the same. haha... unless you're getting jazzy and using an inductor in it.

Oh man... I'm trying hard to remember who uses an inductor in their resonance control.... Is it Mesa?

the main one i know is bogner

I'd like to see that schematic.

[Dmoney]

I'll see if I can find it. whatever I have has no values i don't think. I know the inductor is custom wound.
I have another schem or two that have inductors in the NFB. I can send you those. The idea was probably taken from the Uberschall.

[JacksonRR]

Yeah the only Uber scheme I could drudge up was on SLOClone forums and you know how they work. They'll post up incomplete schemes and then talk about what's correct or not. It's a 34 page thread if you care to sign up and read it. No one knows the actual specs of the inductor though. One member had success using the inductor from a wah-wah on a Marshall rebuild.

[Dmoney]

the OD3 and OLS schem on that forum both contain inductor based depth circuits. I don't know the Uber values either. I just have the layout somewhere.
I just ordered a set of the IG/Shinrocks. Will post some pics of how they look.