DrZ KT45

[funkmeblue]

bassman iron is to low of voltage 370-0-370 is what is needed

[dave g]

bassman iron is to low of voltage 370-0-370 is what is needed

Uhh, no, I don't think so.

I wouldn't put over 500 volts on KT66s. Bassman iron will get you right around 450, right where you want to be.

Please tell me where you are getting these numbers from.

[funkmeblue]

why no, is the schematic wrong for the root 66 and the leak? A bassman transformer is 325-0-325v. What am I missing? thanks

[funkmeblue]

that gives about 445vdc for b+1 after the gz34

[funkmeblue]

the leak is 380-0-380v and the z schematic I have which very well could be wrong says 370-0-370v, the groove tubes kt66 hp can handle plate voltages up to 550 volts. If these higher voltages were true, what would that do to the output inpedence?

[dave g]

A GZ34 has an internal resistance of around 175 ohms. Figure around 85mA current draw at idle for the entire amp - so the voltage drop across the rectifier will be in the neighborhood of 15 volts (pretty normal). A 370-0-370 transformer will get you close to 520 volts RMS, so even after the GZ34 you're looking at 500 volts.

Bassman iron will, as you said, get you in the very happy neighborhood of 440-450 volts.

Notice the extra series resistance after the rectifier in the Leak schem.

I don't know about that Z schematic. A 75 volt drop across a GZ34 isn't right.

Even at 550v, the output impedance isn't gonna shoot up to 8k, that's for sure.

Honestly, I'm not telling you not to build the amp as you see it on paper. I'm just saying that in my experience, I wouldn't trust most new production tubes to hold up to their theoretical max ratings. YMMV.

[funkmeblue]

I'm just interested in the output section of this amp, I guess jtm 45 Iron or bassman should surely work. I want to go cathode bias, the leak 25+ states that is can run el34, kt66 and 5881 without any changes and has a 7k output impedence

[dave g]

I'm not saying 7k won't work - with tubes, pretty much anything will work. It's not optimal, though. Read the tube datasheets - KT66s want to see 5k. Hooking up an A470 wacky so that you get 8k on the primary is pretty silly when you have a 4.3k primary to begin with...

[M Fowler]

Yeah I got the wrong photos oh well, sorry. So I will have to make up for that with some attachments.

Mark

[dave g]

I see our friend Z is putting the good old "tube condom" to good use

[funkmeblue]

475 volts 5k 50 watts fixed bias
450 volts 8k 30 watts cathode bias
according to the data sheets, see why I'm confused, and to add to that they are in ultra linear mode
this info from 1956 marconi

[funkmeblue]

safety first, std's mess with the transients

[M Fowler]

I am having trouble with the RT 66 BOM but maybe this time it will upload. No it must be to large or wrong file ext. so I hope it OK to do it this way.

Mark

DR Z ROUTE 66 AMPLIFIER BOM

V1 EF86
V2 12AX7
V3 KT66
V4 KT66
V5 5AR4
Jacks 12a input 1 L11 Spkrs 3
Pilot lite 120v red
knobs 3
Vol 1MA
Bass 1ML
Treble 1ML
IED plug power
Fuse holder Fender type 2A
Pwr Sw 1
Stby Sw 1
PT 120v 370v/0/370v/6.3v
OT
chassis aluminum 16x8x2.5
cap 10uf 150v electrolytic Mallory 2
cap 0.15uf 150v electrolytic Atom 2
cap 25uf 25v electrolytic Atom 1
cap 1000pf Mylar 1
cap 0.022 orange Mallory 1
cap .1uf orange Mallory 3
cap .0068uf 400v white 1
cap .0047uf orange Mallory 1
cap 0.047 orange Mallory 2
cap 50 500v electrolytic 2
cap 47 500 electrolytic 1
cap 0.01uf orange Mallory 1
cap 100pf Mylar 1
Bais 50K bias pot 1
Res 1.0 ohm 2
Res 470 3w 2
Res 27K 2
Res 100K 1
Res 68K 1
Res 1M 4
Res 150K 1
Res 2.2K 1
Res 220K 3
Res 47K 2
Res 1.2K 1
Res 82K 1
Res 91K 1
Res 10K 2W 1
Res 15K 1
Res 5.5K 1
Res 1.5 3w 2
Diode In4007 1

[dave g]

Yes, you are right, I was quoting specs for fixed bias.

UL would be 8k as you said.

[funkmeblue]

so if I only wanted 8ohm and 16 ohm speaker taps I could offset the dynaco transformer and get 8.6k. I have a 45 watt heyboer from weber in my express that can be either 3.4k or 6.8k and works great