Search found 2313 matches

by tubeswell
Wed Dec 11, 2019 7:43 pm
Forum: Technical Discussion
Topic: output transformer primary impeadance
Replies: 19
Views: 2557

Re: output transformer primary impeadance

I’m sorry Martin. I was wrong and got current phase confused with turns direction. I must be suffering from some kind of mental fatigue.
by tubeswell
Mon Dec 09, 2019 7:27 pm
Forum: Technical Discussion
Topic: output transformer primary impeadance
Replies: 19
Views: 2557

Re: output transformer primary impeadance

wpaulvogel wrote: Mon Dec 09, 2019 6:53 pmI’m pretty sure the primary is all wound in the same direction. Once half of the primary is wound, they pull off the center tap, then go back to winding, same direction.
Yep that’s looking at the winding from another direction. :wink:
by tubeswell
Mon Dec 09, 2019 5:23 pm
Forum: Technical Discussion
Topic: output transformer primary impeadance
Replies: 19
Views: 2557

Re: output transformer primary impeadance

Put AC into the secondary of an OT and you can measure AC plate-to-plate on the primary. Yes they do, but on the scope the two primary ends will be in opposite phase. While one winding end peaks, the other winding end troughs, yet the phase being sourced from on the secondary is the same. The only ...
by tubeswell
Mon Dec 09, 2019 3:35 pm
Forum: Technical Discussion
Topic: output transformer primary impeadance
Replies: 19
Views: 2557

Re: output transformer primary impeadance

The turn phase is opposite in each half of the primary. It has to be, because the current phase is opposite in each half of the primary, yet in the same phase in the secondary. The only way it can do this is if the turns on one half of the primary go in the opposite direction to the other half. (Thi...
by tubeswell
Mon Dec 09, 2019 7:24 am
Forum: Technical Discussion
Topic: output transformer primary impeadance
Replies: 19
Views: 2557

Re: output transformer primary impeadance

hey fellas, can some one tell me what the primary impeadance would be when using a 4k -16 ohm output transformer in a single ended configuration by ignoring the center tap. thanxxx A PP OT has one half of the primary winding wound with the turns going in the opposite direction to the other half of ...
by tubeswell
Sun Dec 01, 2019 5:57 pm
Forum: Technical Discussion
Topic: Spitfire filtering vs 18w
Replies: 8
Views: 1194

Re: Spitfire filtering vs 18w

Generally the PI is considered part of the power amp, and has much higher current and potential for sending noise into the preamp, ... Its actually about the same current as a pre amp tube for both triodes (in the above schematic, 62V/48k2 = 1.3mA going through the cathode at idle) (FWIW I too pref...
by tubeswell
Sun Dec 01, 2019 3:03 am
Forum: Technical Discussion
Topic: Mojotone JCM800 50 watt output transformer
Replies: 8
Views: 926

Re: Mojotone JCM800 50 watt output transformer

Got the transformer. Checked the turns ratio and it’s actually 3.8k and change on all 3 taps. Installed it and the amp made 49 watts now and 400 volts on the plates at idle. Man this thing sounds awesome! Played it for about an hour and I’m really satisfied and can’t hear shit! Good voltage/power o...
by tubeswell
Sat Nov 30, 2019 11:46 pm
Forum: Technical Discussion
Topic: Does Feedback Need to Change When Pulling Two Output Tubes?
Replies: 8
Views: 924

Re: Does Feedback Need to Change When Pulling Two Output Tubes?

If it is, I guess it would mean that feedback resistors do need to be adjusted to maintain the same amount of feedback in dB and actually get the full dB reduction expected. Anyway it would be only around 2 dB of feedback so probably not so noticeable. Technically yes, but the FB loop resistors mak...
by tubeswell
Thu Nov 28, 2019 10:20 pm
Forum: Technical Discussion
Topic: Fuse Holder Placement
Replies: 11
Views: 850

Re: Fuse Holder Placement

I think it's fine where you've put it. But it sounds like you want to shift it for peace of mind - so do that.
by tubeswell
Tue Nov 26, 2019 6:56 am
Forum: Technical Discussion
Topic: Texas tea mod
Replies: 9
Views: 1576

Re: Texas tea mod

sluckey wrote: Tue Nov 26, 2019 12:18 am
tubeswell wrote: Mon Nov 25, 2019 7:10 pm Is that a more oily sounding mod? 😊
You may be thinking about black gold. :mrgreen:
Image
by tubeswell
Mon Nov 25, 2019 7:10 pm
Forum: Technical Discussion
Topic: Texas tea mod
Replies: 9
Views: 1576

Re: Texas tea mod

Is that a more oily sounding mod? 😊
by tubeswell
Tue Nov 19, 2019 4:26 pm
Forum: Technical Discussion
Topic: 6L6GC Power Tube Matching
Replies: 23
Views: 2622

Re: 6L6GC Power Tube Matching

The main benefit of matching output tubes for current draw in a guitar amp, is to minimise hum noise when the amp is idle. A bit of mismatch won’t harm the tubes (provided they aren’t drastically mismatched).
by tubeswell
Fri Nov 15, 2019 11:16 pm
Forum: Technical Discussion
Topic: Output safety resistor
Replies: 4
Views: 589

Re: Output safety resistor

Handy for those 'in case' moments (if someone forgets to plug the speaker in or the speaker coil goes open). A permanent resistance across the secondary doesn't do any harm if the resistor is sufficiently high resistance to not affect the reflected load, nor divert output power away from the speaker...
by tubeswell
Fri Nov 15, 2019 10:44 pm
Forum: Technical Discussion
Topic: Amp Design - Single Ended Output Power..
Replies: 15
Views: 2581

Re: Amp Design - Single Ended Output Power..

Figure a (very) rough guide where output power will be about 0.4X the rated plate dissipation of the output tube. So for a 50W output, you'll need 125W worth of plate dissipation. (And then there's all the other stuff - optimum load vs peak Ig2, amount of driving signal at the output tube grid vs ou...
by tubeswell
Sun Oct 27, 2019 1:19 am
Forum: Technical Discussion
Topic: How to install metal corners
Replies: 13
Views: 4157

Re: How to install metal corners

Iron Works wrote: Tue Oct 22, 2019 10:27 pm I build many cabs and I've made a handy jig for the countersunk corners given they won't sit flat until you remove some material for the countersunk location. I've attached a photo of my jig and how I marked the locations for the holes.
Nice jig.