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Need advise, replace 6x4 with 5Y3 or 5U4G

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Hello,

Been here for years but reading most of the time, now want to seek advise on my 5670 pre-amp, originally using 6x4 as rectifier, since I want to change it to 5Y3 (JJ have new 5Y3 tubes) , using 5U4G is an overkill, but I got better choice for quality tube.

I'm not good at the circuit, I can read but dare not to change, I know the value is different, they're not interchangeable. At that time I got help from a friend to finish it, I don't really know how to calculate. And he move to 80 and left no 6x4 circuit diagram for me, below was the "new version" already using 80, and "old version" of the pre-amp inside, I've already replace the power with Tango ISO and the sound become more solid and more energy. I've regret not taking a high resolution photo of the latest one.

Thanks for any suggestion.

5670_OPT2(Voltage).png


Iux1fLuTC_jDpqpK31QzIkLpRO53Ai5VVgTqaUDOqUUlAgX57v_KTMuaFEaSIrZOJRhaTLiybn7gqENvWoMgXg0qxkTjJQhaiAnqn3uYMMcHF7DJ2IUXYTsMbEfpahXSqb21uh8DMWd1y84UwaUlULc6AmqQeYnxc3qaEwXpGBJK6kcibQtfICe5UHAO6XZQkxghWXlad4gL1jaz1qQyKUDdffp5G1FM4EekvU_k_GIt30b29QdTOkmN5KwbHQa7pxmug8ZHipkWyT5t9lBBQzvuuh-M55bYUngx9T77yWWyvifsfgVzTBDo-eCg-5VHm5g49-aa-TjJg9SH6w8MsUZLO4ji3tEDkihTHzoE7iNaoxYO7Hc-iwY16SEm7uepbdcqyDk1Y-NbZMFZEgWgIF8PSW1FbzSiiifaY_bTUpzy4ttTEfy8zKfd1nM78rTpN69R9Teu7XdfMGLtWeqkWLRVl04bKU4ipgV0NcTphwGXwZ2Op3CpujsaeV3NpBuFzb61av8u2JFluq8ixkVWnOckTKBR0jU_7rArcRo59nHqEWAR9MMJcaK-7azX8vtGh6bYNXkO9uq5_4ftOSsmGD4o6RWjY6BQN15r1vjgSk5iOaPJN4QgVAJ64dtCGUZs=w707-h481-no
 
Perhaps (probably) the original design used a 6X4 because it can run off the common 6.3V filament winding of the other tubes. The 6X4 does not need a separate 5V winding.
The 80, 5Y3, etc. need a separate 5V winding (more transformer, more money).
Design to a price point.

The delayed B+ might be more important for Certain types of power output tubes, and not needed for most line preamp tubes, and for many output tube types.
I use solid state diodes (horrors) in my B+ supplies. The quick turn on B+ is not currently causing me any problems in those amplifiers.

If I was to use tube rectification, I would prefer the directly heated types, 5Y3, etc.
I would not be likely to use the indirectly heated 6X4, 5AR4, etc.
 
Delayed heater can also mean the difference between needing 450V caps throughout the entire amp power supply vs only 250 downstream of the filter.

Saving a few bucks this way isn't optimal but it happens a lot in production hardware where a few bucks per amp means tens of thousands down the road.
 
kylej1050,

Good Point.

That is why all of my B+ caps are rated for 500V, I use solid state rectifiers.

All my amps use Bleeder Resistors; and I wait for the caps to discharge before working on them (and I use a DMM to be sure there is no voltage left in the caps).
Safety First.
 
Perhaps (probably) the original design used a 6X4 because it can run off the common 6.3V filament winding of the other tubes. The 6X4 does not need a separate 5V winding.
The 80, 5Y3, etc. need a separate 5V winding (more transformer, more money).
Design to a price point.

The delayed B+ might be more important for Certain types of power output tubes, and not needed for most line preamp tubes, and for many output tube types.
I use solid state diodes (horrors) in my B+ supplies. The quick turn on B+ is not currently causing me any problems in those amplifiers.

If I was to use tube rectification, I would prefer the directly heated types, 5Y3, etc.
I would not be likely to use the indirectly heated 6X4, 5AR4, etc.


I like direct heater, the sound is 'usually' better.
Someone said can use a resistor to down the heater 6.3V to 5V, I didn't try that yet, and don't know if any downside.
 
Someone said can use a resistor to down the heater 6.3V to 5V, I didn't try that yet, and don't know if any downside.


Before considering this, you'll have to pay attention at two points:


- Does the x-former have a separate winding for the 6X4 heater? Otherwise your suggestion won't work.
- Does the new tube draw a heater current of not more than 0.6 amps? Otherwise most probably your suggestion won't work.


Best regards!
 
Yes,

Direct heated rectifiers do require a separate filament winding.
Otherwise, how would you like 350V on all the other tubes filaments in the amp.

Some indirect heated rectifiers have a direct connection from the cathode to one end of the filament. That also requires a separate filament winding. The 5AR4 is one such rectifier tube.

Some indirect heated rectifiers do not have a connection from the cathode to the filament. The 6X4 and 6X5 have those cathode connections that are separate from the filament connections.
That does not require a separate filament winding. Simple, and less expensive.
But . . . if that filament to cathode insulation ever breaks down, you will most likely need to replace all the other tubes too.

Now you know why I prefer directly heated rectifiers with separate filament windings.
 
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Kay Pirinha,

Agreed. I use SS rectification.

As I said in post #11, IF I was to use tube rectification, I prefer indirect heated rectifiers.

But as direct or indirect rectifier heating in products I owned, I have experienced more arcing with indirect heated rectifiers (and more ofter hear about arcing with indirect heating).
So many 'designs' go beyond the tube rectifiers maximum ratings, and then they wonder why they are having problems.

For really stiff sag proof, regulation is needed, but I do not make my amplifiers that complex.
I like simplicity (my tradeoff).
 
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