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Starting a SSE build

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If you don't plan on using the SS rectifier D1 and D1 and the switch are not needed and could be left out. All three are needed for the SS option. The diodes are switched in parallel with the tube when the SS rectifier switch is engaged, and since they have far lower loss that the tube virtually zero current flows through the tube. The tube can be removed in this mode, but it is not necessary unless you want to save about 10 watts of power (it's heater).


They do a 47uFat 600v but only 100uF or 200uF, both at 550v. I had been thinking of using the 200uF in C2.

200 uF for C2 is OK. My builds have used a 100 uF electrolytic in parallel with a 100 uF polypropylene motor run cap for a total of 200 uF. An all polypropylene solution is good too. Too expensive for my builds though.

D3, D4 and the CL140 were added to reduce the stress on the 5AR4 when the amp is first switched on. There was a period of about 2 years when both the Chinese and Russian 5AR4 tubes had serious quality issues. It wasn't uncommon for a new tube to blow up on power up. Some builders prefer to install jumper wires in these component locations (fear of silicon). Your build will operate the 5AR4 near its maximum ratings so these parts are recommended.
 
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There are 3 new components on the new board. If you really want your board to be exactly like the old board all 3 can simply be replaced by a jumber wire made from a resistor lead.

D3 and D4 are indeed 1N4007. I suppose a purist will use an UF4007 but it shouldn't make any difference since the rectifier tubes characteristics dominate.

TR1 is a GE CL140.

These are my choices of CL-140 (see attached). Are either of them suitable for the TR1 position? Also, any idea why the straight lead version is so ridiculously priced?

By the way, my board arrived today, George. Thank you! It is beautiful.
 

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Are either of them suitable for the TR1 position?

They are actually both the same part, the only difference is the leads.

any idea why the straight lead version is so ridiculously priced?

Likely a screw-up in the data entry department.....The data sheet gives 3 different numbers, the CL-140 with plain straight wires, the CL-140A with the kink to space it off the board, and the CL-140B on tape and reel.
 
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They are actually both the same part, the only difference is the leads.

I sort of figured that, but I have learned the hard way not to assume anything when it comes to electronics.

Likely a screw-up in the data entry department.....The data sheet gives 3 different numbers, the CL-140 with plain straight wires, the CL-140A with the kink to space it off the board, and the CL-140B on tape and reel.

Makes sense. So, since you didn't explicitly warn against using either of these parts, I'll go ahead and order the kinked-lead version.

One other question, George - with the inclusion of these three new parts (to protect the rectifier tube) do you still think it is a good idea to put an inrush limiter on the main power transformer primary (between the power socket and the primary) ?

Many thanks, as always, for your help!
 
The Inrush Current Limiter on the transformer primary is there mainly to blunt the huge turn on surge when all the tube heaters are cold. Theory says it should prolong the life of the heater in the tubes, but today's tubes will usually die of another cause long before the heater dies......When was the last time someone here changed a tube because it's heater went open?

A Directly Heated Tube however, is a different story due to the physical stresses involved when taking something through several hundreds of temp change in a few seconds. I have had a few of the early Russian 300B's fail due to half the filament going open.

The ICL is up to you on the SSE, I typically don't use them. I do use them on TSE's and other DH amps, BIG tube amps of all kinds, and anything using a solid state rectifier just to prevent the occasional fuse blow on power up.
 
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The Inrush Current Limiter on the transformer primary is there mainly to blunt the huge turn on surge when all the tube heaters are cold. Theory says it should prolong the life of the heater in the tubes, but today's tubes will usually die of another cause long before the heater dies......When was the last time someone here changed a tube because it's heater went open?

A Directly Heated Tube however, is a different story due to the physical stresses involved when taking something through several hundreds of temp change in a few seconds. I have had a few of the early Russian 300B's fail due to half the filament going open.

The ICL is up to you on the SSE, I typically don't use them. I do use them on TSE's and other DH amps, BIG tube amps of all kinds, and anything using a solid state rectifier just to prevent the occasional fuse blow on power up.

Thanks George.

I plan to implement switchable SS/tube rectification and I also will be trying some DH rectifiers (5U4 variants), so perhaps it makes sense to just go ahead with the ICL on the primary.

Am I right that there is no downside to the ICL on the primary? The one I have chosen ( MS22 12103-B Ametherm | Mouser Canada ) is $6. Seems a small price to pay for some extra protection.

By the way, is the rectification switchable while powered up, or is this something that needs to be selected before power up? Same question goes for the other switch options (Triode/UL, CFB) ?
 
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