I would go for the Sowter 8424 because you can find its perfomance for your specific application in its datasheet. In such case use 20K for R8 (primaries in parallel). If possible, you might want to specify lower DC current as you don't need 60 mA primary DC current (primaries in parallel). 15 mA for primaries in series and 30 mA for primaries in parallel will be enough. This way primary inductance will be higher. I suppose this would be regarded as a custom order but the price shouldn't be different.
The Hashimoto could work as well but they usually recommend 1:1, 1:0.5 and 1:0.5+0.5 ratios (i.e. primaries always in series which limits the DC current to max 15 mA and 7-10 mA recommended).
The Hashimoto could work as well but they usually recommend 1:1, 1:0.5 and 1:0.5+0.5 ratios (i.e. primaries always in series which limits the DC current to max 15 mA and 7-10 mA recommended).
I think that if you use 47K would be worse than no gird resistor. In general, whatever value you use the result will not be great at low frequency becuase your inductance is a bit low in all cases. That's why I was telling you to get the Sowter for lower DC current rating and higher inductance.
Another (better) choice would be the Lundahl LL1692a (ALT T connection 2:3.5) that would have 35H and up to 36 mA DC current.
High gain + step up interstage for driving the 845 with low distortion are too many things for a single stage, IMHO.
The closest distributor to Portugal is in Spain:
www: Granada-Audio - Válvulas y Componentes para amplificadores - Transformadores Lundahl
Otherwise ask Thomas (Vinylsavor) in this forum. Maybe he can help you.
www: Granada-Audio - Válvulas y Componentes para amplificadores - Transformadores Lundahl
Otherwise ask Thomas (Vinylsavor) in this forum. Maybe he can help you.
I'm planning on building an 845 monoblock low voltage 845 amplifier ~5 ..15W
that can be connect to 90 db speakers.
about the gain I'd like to be able to connect direct to CD. I can also use a preamplifier(I do not know how much gain will I need)
maybe tow stages will give a better performance.
that can be connect to 90 db speakers.
about the gain I'd like to be able to connect direct to CD. I can also use a preamplifier(I do not know how much gain will I need)
maybe tow stages will give a better performance.
I think you will get about 7W max with 610 total supply voltage at 60 mA and 5K.
If you go for the LL1692a/18mA you can experiment the connection ALT T (36 mA and 35H) with the 6C45 or the connection ALT S 4:3.5 ratio with the D3a.
The connection ALT S will allow 18 mA that are enough for the D3a with 125H primary inductance.
With the 6C45 and LL1692a ALT T you should need less than 0.7 V RMS for full power. With the D3a and LL1692a ALT S you will need about 1 V RMS. For 1W output you will need about 0.25 V RMS in the first case and 0.37 V RMS in the second. This could be enough if you use a modern CD player and 90 dB efficient speakers in most cases without adding a step-up input transformer. I would first try this two stage amp with normal volume control at the input and then if you feel the gain is not enough you can think about increasing the gain further.
If you go for the LL1692a/18mA you can experiment the connection ALT T (36 mA and 35H) with the 6C45 or the connection ALT S 4:3.5 ratio with the D3a.
The connection ALT S will allow 18 mA that are enough for the D3a with 125H primary inductance.
With the 6C45 and LL1692a ALT T you should need less than 0.7 V RMS for full power. With the D3a and LL1692a ALT S you will need about 1 V RMS. For 1W output you will need about 0.25 V RMS in the first case and 0.37 V RMS in the second. This could be enough if you use a modern CD player and 90 dB efficient speakers in most cases without adding a step-up input transformer. I would first try this two stage amp with normal volume control at the input and then if you feel the gain is not enough you can think about increasing the gain further.
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.
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.
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.
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!
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.
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.
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
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
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)
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)
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.
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
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
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.
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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