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Old 19th January 2011, 04:36 AM   #791
GaryB is offline GaryB  United States
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Originally Posted by Nightpuma View Post
No one who has any thoughts on this matter?
I like keeping all iron (transformers and inductors) away from the signal tubes. So I would split the power supply so that only the last C is in the preamp. And I always like to have some C on both ends of the cable connecting the power supply to the preamp. So I'd put something like a 0.1uf after the last L in the power supply and then put the bigger C in the preamp.

---Gary
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Old 19th January 2011, 07:27 AM   #792
massimo is offline massimo  Italy
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Quote:
Originally Posted by GaryB View Post
I like keeping all iron (transformers and inductors) away from the signal tubes. So I would split the power supply so that only the last C is in the preamp. And I always like to have some C on both ends of the cable connecting the power supply to the preamp. So I'd put something like a 0.1uf after the last L in the power supply and then put the bigger C in the preamp.

---Gary
I totally agree.
VGeorge, would you be so kind to describe in detail you PS arrangement?
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Old 19th January 2011, 08:36 AM   #793
vgeorge is online now vgeorge  Greece
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Originally Posted by massimo View Post
I totally agree.
VGeorge, would you be so kind to describe in detail you PS arrangement?
5AR4GU then LCLC (ll1673-47uf-ll1673-200uf) are at the PS case and two SSHV at the pre case. Thinking either move the big cap the pre or put two small caps (0.1uf?) near the regulators.
Heaters supply 15000uf x 2 per channel on the PS box and a 1000 uf at the pre near the regulators.
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Old 19th January 2011, 08:43 AM   #794
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Originally Posted by Nightpuma View Post
Hello all,

I have now almost sourced all the parts for my #26 preamp project. The signal part will be plain with Hashimoto 20K line output transformer. The filament will be regulated with Rod Colemans DHT heater. HT will be LCLCLC. It will be a spilt chassis design, one for signal, one for PS.
Before I make a conclusion on the size of the chassis, I need some advice from you guys:-)
Where would you suggest that I spilt the PS? For filament, I was thinking of putting only the regulator board in the signal chassis. And for HT, I was thinking of putting the last LC in the signal chassis.

What do you think?

Theo
Theo, Keeping the Filament trafo away from the signal tubes & wiring definitely makes sense. But, be sure to keep the rectifier and capacitors close to the trafo - don't use long wires for these, or they will 'transmit' to other circuits! For a 1A regulator, the rectifier-cap CURRENT pulses may be 5A, with fast rise time. Using the names in my application note AN-DHT01 for the filament heater, C1-R1/R2-C2 should be in the PSU chassis.

Then, when you mount the filament regulator (near to the tubes), use a 1000uF 16V Panasonic FC or your favourite low impedance elko. Mount this on the regulator PCB, like George has done.

The same approach with the B+ PSU is recommended.

Keep the filament supply wiring away from the B+ wiring, when you connect the PSU chassis to the Signal Chassis.
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Old 19th January 2011, 09:01 AM   #795
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Originally Posted by merlin el mago View Post
Who knows where to buy the LL1660 cheaper than in K&K Audio
Lundahl's website:
Lundahl Transformers Distributors
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Old 19th January 2011, 09:07 AM   #796
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You are a crack
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Old 19th January 2011, 12:55 PM   #797
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Hi - vgeorge mentioned 5AR4 as a rectifier, and it may be interesting to compare notes about preferred rectifiers.

I've gone over to directly heated rectifiers - with DHTs I don't see the point of slow startup unless I'm missing something. Anyway, they sound better to my ears.

I'm having good sound with 5Y3 (80) or AZ1 mesh in my preamp. In my 300b SET amp I've been using 5U4G (5Z3) or recently a RCA 5T4 which surprised me since it's an ugly metal thing but actually has several strong points to the sound.

I've put all my Mullard GZ32,33,37 on ebay this week.

What are your experiences?

Andy
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Old 19th January 2011, 01:24 PM   #798
massimo is offline massimo  Italy
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I'm planning to use a RCA #80 as rectifier, but iI would also like to try a Mullard GZ37 (I'm having a custom xfrm wound with 5 and 6.3 V sec).
Do you think it will be a waste of time as the #80 is clearly better?
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Old 19th January 2011, 03:45 PM   #799
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The 80 and GZ37 are quite different - 80 is lower power direct heated, GZ37 is higher power indirect heated, more for larger amps like 300b SETs where it's popular.

If it's just for a preamp, the lower power rectifiers are nice like the AZ1 mesh and 80. If you're running the preamp and amp off the same supply, then try the 5U4 or 5T4 in octal. If you're using a 4 pin socket then you have the 5Z3 as a 4 pin alternative to 5U4G. I doubt if you'll miss the GZ37.

Andy
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Old 19th January 2011, 04:16 PM   #800
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Hi Theo,
Quote:
Originally Posted by Nightpuma View Post
Where would you suggest that I spilt the PS? For filament, I was thinking of putting only the regulator board in the signal chassis. And for HT, I was thinking of putting the last LC in the signal chassis.
That's how I would do it. In my case since I'm using LCL passive filtering for the filaments, I keep the last L of the filament supply and the last LC of the B+ supply in the preamp chassis. All the rest of the PSU goes to a separate chassis.

Best regards

Thomas
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