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Cheap (5) SE Tube amp kit, transformer and chassis on ebay
Cheap (5) SE Tube amp kit, transformer and chassis on ebay
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Old 19th October 2011, 10:49 AM   #51
data is offline data  Australia
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Those voltages are a worry.

This is the problem with 220v amps here in Australia.
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Old 19th October 2011, 11:53 AM   #52
aspringv is online now aspringv  Australia
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Cheap (5) SE Tube amp kit, transformer and chassis on ebay
Default 245vac - Yeilding some,er, exciting, voltage numbers

So I powered up the default psu circuit and got...

B1 - ~490V
B2 - ~478V
B3 - ~134V

Given to date I've only ever built transistor amps, I'm still moving my brain up an order of magnitude in terms of expected voltages...

OK, so this has arisen due to the secondaries being 330V (not the 290V on the original schematic), and the mains being 245VAC instead of Australia's nominal 230VAC...

So, can I throw this one out to the collective Diyaudio brains trust? The target voltages in the Ezekiel circuit are B1 278V, B2 260V, so I'm a hell of a long way over these... What to do?

Last edited by aspringv; 19th October 2011 at 12:11 PM. Reason: I'm a numpty
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Old 19th October 2011, 12:34 PM   #53
rock4016 is offline rock4016  United States
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Did you put a 140 mA load on your test power supply to allow for a voltage drop through the various components?

Once you do that you can usually add another RC stage and drop the B+ to your desired level.
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Old 19th October 2011, 12:44 PM   #54
iko is offline iko  Canada
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Cheap (5) SE Tube amp kit, transformer and chassis on ebay
Quote:
Originally Posted by aspringv View Post
First up, the local mains is at 245V AC, whilst the transfo is wired for 220vac so all the secondaries are running a little high.
5v nominal- 5.8vac
6.3v nominal - 7.4vac
330v nominal - 365vac
So I'm a little concerned about these readings - I'll finish it all up and see what they read loaded.
This might help with your mains problem:

http://www.apcmedia.com/salestools/M...9K8V_R0_EN.pdf

APC Line-R 600VA Automatic Voltage Regulator, Schuko Outlets, 230V
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Old 19th October 2011, 01:14 PM   #55
aspringv is online now aspringv  Australia
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Cheap (5) SE Tube amp kit, transformer and chassis on ebay
Nope, no test load as it currently stands - I just ran a multimeter over the various points on the psu circuit.

Reckon it's about time I learn a bit about proper design of low pass filters I suppose.

That said I was looking at buying a variac sometime soon anyway...
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Old 19th October 2011, 04:10 PM   #56
aspringv is online now aspringv  Australia
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Cheap (5) SE Tube amp kit, transformer and chassis on ebay
Default how far to go

Is anyone able to suggest maximum reasonable values for B1, B2 and B3?

And can anyone speculate the current draw on the supply from each of these points?

I've been playing about with simulations of the psu circuit and in order to see what I'm up against in terms of RC filters and subsequent total current draw. To really get a feel for whats going on these values would be helpful if anyone could assist?

I might just summarise my various plea's for help shortly
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Old 19th October 2011, 05:12 PM   #57
costis_n is offline costis_n  Greece
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Places of 1/4 Watt resistors: 100K in the 1st triode, 270K in EL34 grid, 4K7 in feedback network.
Other : Better with 330R in EL34 cathode, esp. considering your high line voltage. No time to do any calculations yet.
Also: I do not see ant gridstopper resistors.
I cant remember if it has been mentioned, but better way is to have one 6SN7 as the "upper" valve in both channels ans the other 6SN7 as the "lower" one. That way you stress less the cathode-heater insulation.
That's it for now, maybe I ll think of more later.
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Old 19th October 2011, 06:19 PM   #58
VictoriaGuy is offline VictoriaGuy  Canada
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Cheap (5) SE Tube amp kit, transformer and chassis on ebay
As Costis has mentioned, the EL34 cathode resistor 'controls' the current flowing through the power tube, so if you increase the B+ voltage you will need to increase the resistor value to keep the currrent the same. (Ohms law). It's pretty common to have to tweak/adjust the cathode resistor value to keep the plate dissipation (in watts ie volts x amps) within limits.

I wouldn't get too excited about the higher voltages until you power up the amp with tubes (and dummy load or speakers). The power transformer supplied with my 'kit' is 'just big enough' to do the job, and I'd expect to see a voltage drop once it is put to work.
As rock4016 suggests, dropping the B+ is fairly simple. If your heater voltages are much over spec, that would be a bigger problem, I think, as it can reduce tube lifetime.
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Old 20th October 2011, 12:58 PM   #59
costis_n is offline costis_n  Greece
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Or, if you want to do something a little different, same tubes but without global feedback, ask me!
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Old 20th October 2011, 01:22 PM   #60
data is offline data  Australia
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I hate GNF, It's the devils evil twin
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