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Old 14th February 2014, 10:40 AM   #11
45 is offline 45  Italy
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MFF, I don't know TJ 845. I know the 845 Golden Dragon that basically is a GE copy. This is quite good if properly selected.
Due to massive production with minimal quality control for the general market, Chinese tubes can be quite good or really poor. For just one pair I would spend a bit more and buy them from a reputable seller.
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Old 14th February 2014, 11:21 AM   #12
MFF is offline MFF  Portugal
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I've found this tow seller...
Tube-Shop.com - Vacuum Tubes for Hi-Fi, Guitar and Radio amplifiers
And TJ Full Music 845 valves Hifi Collective
sorry to bore you with these, but these things are very expensive.
I'm trying not to make a rookie mistake.
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Old 14th February 2014, 11:49 AM   #13
45 is offline 45  Italy
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Quote:
Originally Posted by MFF View Post
I've found this tow seller...
Tube-Shop.com - Vacuum Tubes for Hi-Fi, Guitar and Radio amplifiers
And TJ Full Music 845 valves Hifi Collective
sorry to bore you with these, but these things are very expensive.
I'm trying not to make a rookie mistake.
I don't know those. Not sure those metal plates are worth that money. Maybe wait for someone that has them and can tell you. I was referring to the GE copy with graphite plate. It has not been in production since sometime ago but still available in some local shops.
However I think you can buy original NOS GE for that sort of money!
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Old 14th February 2014, 12:20 PM   #14
45 is offline 45  Italy
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This is it:
Electronic Tube and Valve Product Details

Except the brand they identical to the GD I was talking about. Billington is a reputable seller and his gold series is very good.
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Old 17th February 2014, 11:11 AM   #15
MFF is offline MFF  Portugal
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Hi,
I ordered a pair of Gold Billington 845, thanks for the help!
Now I'm struggling to find a good pair of output transformers.
I was looking in to Hashimoto H-20-7U,
But European supplier do not have for deliver(takes at least 6 weeks)
Is contact at Japan is in the Hospital for at least 6 weeks,so a big unknown here.
Tango is no longer on the market..
I found some possibilities on ebay but thei are from Japan or US and I don't now how much will I pay customs tax.
Do you now a good alternative or a supplier?
Many thanks
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Old 17th February 2014, 12:24 PM   #16
45 is offline 45  Italy
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I think if you write to Hashimoto and tell them about your incovenience they might ship directly to you. Likely you still need to take into account custom tax on top of that price.
Otherwise if you buy the LL1692a you might look at Lundahl OT's as well. There are some that are good for you application:
1) LL1623 (5.6K for 0.2 dB power loss) with 2 useful gap values for DC current : 60mA and 46H inductance or 90 mA and 30H inductance.
2) LL1620 (11.5K for 0.2 dB power loss or 6K for 0.5 dB power loss) with gap value for 60 mA and 60H inductance. This might be also useful if you go for the 211 or 845 at 1000-1200V/60 mA with 11.5K load.
3) LL1691 is specific for 845 for high power/ high voltage amp (It is 9K with 70mA and 75H)
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Old 17th February 2014, 04:11 PM   #17
MFF is offline MFF  Portugal
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I need some help with maths.
If I choose LL1623 5,6K what is the power that will have on output?
The bias of the 845 are 70V/60mA.
I'm limited by the power supply I have a 370Kx Hammon 250-0-250
If my bias are 60mA I have to use the 90mA gap, am I right?

Thanks
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Old 17th February 2014, 04:42 PM   #18
45 is offline 45  Italy
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Quote:
Originally Posted by MFF View Post
I need some help with maths.
If I choose LL1623 5,6K what is the power that will have on output?
The bias of the 845 are 70V/60mA.
I'm limited by the power supply I have a 370Kx Hammon 250-0-250
If my bias are 60mA I have to use the 90mA gap, am I right?

Thanks
No, you can use it at 60 mA. 90 mA is just a recommended max DC current.
The Pout with 5.6K (actually a bit more) will be slightly less than with 5K. As the Pout of your amp will be around 7W you can go for both as the LL1623 is specified for 13W @30 Hz for the nominal impedance and running at the specified DC current.
The real difference will be distortion at low frequency but is difficult to tell precisely because if you go for 90 mA gap the DC induction will be lower if you run it at 60 but the inductance is 30H. In the other case you run it at higher DC induction but inductance is 46H. Distortion at low frequency depends on both induction and inductance.
Probably with those C cores the 60mA/46H is a bit better as your Pout is only 7W.
If you want to use it in other applications where you need more than 60 mA then it is better to go for 90 mA.
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Old 26th February 2014, 03:18 PM   #19
MFF is offline MFF  Portugal
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Hi
Today I finished the power supply, the first tests were made ​​without any load, my caps are for 1600V.
I have 710V ​​without load, my main transformer are 500V 300mA and I'm using the CT of the filaments to get the HV.
The rectifier tube is 5AR4.
This supply is only for one channel.
Instead of putting a resistance to lower the voltage to 610V it is possible to bias the 845 tube with this voltage(710V), I'm gonna use a borrowed OTP JS_6123HS.(5K)
what value should I use for the cathode resistor, the cap should maintain the same value 20uF?

Thank you for the help.
Regards,
Miguel
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Old 26th February 2014, 07:58 PM   #20
MelB is offline MelB  Canada
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Miguel:
Under load with the 5AR4 I would use about 675v for my calculations. That is about where you will end up.
Yes you can bias the 845 with that voltage. Your output transformer is rated 90mA. I would bias the 845 with about 80mA. (Your power transformer is plenty beefy) I would try with the 1100 ohm cathode resistor you have in the schematic and also with a 1200 ohm which should do it.
That's just the way I would try it. Also maybe a 40uF cathode bypass. This all becomes a matter of what you like.
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