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Tubelab Discussion and support of Tubelab products, prototypes and experiments

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Old 5th September 2020, 01:24 AM   #831
itsikhefez is offline itsikhefez  United States
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Join Date: Aug 2015
After a 14 year run, the TSE must DIE!
There was some discussion here earlier about using CL-90's.
If using a power transformer with dual primaries in parallel (for 120V), do you use a single CL-90 between the switch and one pair of primary wires (or between the fused L terminal and switch),

Or dual CL-90's for each primary winding? The dual CL-90's arrangement is what I've seen in the Firstwatt F5 build guides, as here:
Firstwatt F5 amplifier v3 - diyAudio Guides
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Old 14th September 2020, 10:35 PM   #832
winggo is offline winggo  United States
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Have my 300B amp up and running now for a few weeks. The detail is very good but it seems to emphasize the higher frequencies to the point of being schril. I have it running through an old Nikko SS preamp. That sounded the best out of the three I tried. Have the treble way down and the base up, but the high notes are really hot. Speakers are 96db Sonist Audio. Any suggestions where I should start to look for solutions?
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Old 14th September 2020, 10:39 PM   #833
itsikhefez is offline itsikhefez  United States
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After a 14 year run, the TSE must DIE!
Okay maybe this is obvious but is it surely the TSE and not something else like speaker positioning, the preamp, or source?
If you have a sound card analyzer, you could run a frequency response plot and see if indeed the curve of the TSE is tilted up.

Which 5842 tubes are you using? I found some subtle differences between Amperex Gold Pin, Raytheon 5842 and Western Electric 417A.

Which output transformers ?

And... what is the source?

EDIT: attached is the FR with Gold Lion PX300B tubes... pretty flat.
Attached Images
File Type: png FR LEFT.png (58.4 KB, 302 views)

Last edited by itsikhefez; 14th September 2020 at 10:43 PM.
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Old 14th September 2020, 10:45 PM   #834
itsikhefez is offline itsikhefez  United States
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After a 14 year run, the TSE must DIE!
I guess I should have also asked what is the OPT primary (3.5K or 5K), B+ and 300B bias ?
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Old 15th September 2020, 04:08 PM   #835
winggo is offline winggo  United States
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Before this amp I was using a Jolida integrated with EL35s. Sound was very good, no shrill to it. Put the TSEII together and tried: first a custom switch box with just input switch and volume. Couldn't any volume out of it. Next tried old Easter Electric Mini Pre but that has problems I need to fix. Then used the Nikko pre and that sounded the best of the three. Yes the preamp might be part of it. I will have to hunt up another to test that out.

5842 tubes are Raytheon. Source is DVD and Vinyl.

Output transformers are Eletraprint SE 3k @ 100ma.

I can't remember what the B+ volts were or what I set bias at. I will hook up multi meters tonight and check them out.

The only rectifier tube I could get on short notice was a Groove Tube 5ar5 at the Guitar Store. I could try a better tube there.

Last edited by winggo; 15th September 2020 at 04:12 PM. Reason: forgot point
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Old 16th September 2020, 06:56 AM   #836
itsikhefez is offline itsikhefez  United States
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Join Date: Aug 2015
After a 14 year run, the TSE must DIE!
At this point it would be hard to pinpoint the exact issue.
If it were me, I'd try to rule out as much variables as possible.
Starting with the source, if you have a cellphone or small portable player you can use that as your source/preamp (assuming it has volume control).

I recall that if the 300B is under-biased the sound can be shrill, so I would double check where you're at. Depending on your B+, that could be anywhere between 60mA and 90mA.

Also double check the 5842's are set at 175V.

If all of that checks out, then could be a speaker impedance mismatch. If your speaker impedance is mostly below the tap you're connected to, you'll have less than 3K at the 300B which is probably not optimal.
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Old 7th October 2020, 03:29 PM   #837
sunil is offline sunil  India
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Total newbie here. I'm about to start the TSE-II (300b) build and had a question, wondering if you can help.

The mains trafo is a local build. It is spec'ed at 310-0-310@225mA and winding resistance is 60R (measured from 310 to 310 tap). I'm looking at between 370-380v with a choke. Will this cause problems with a GZ34 ?

How do I go about calculating the choke value? What should I do? Please help.

Last edited by sunil; 7th October 2020 at 03:33 PM.
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Old 9th October 2020, 10:08 AM   #838
sunil is offline sunil  India
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Join Date: May 2003
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Can someone please help answer the trafo resistance question. Think I can work the rest.

The resistance on one half of the transformer secondary is 30R and the GZ34 spec sheet mentions ~100R (~350V). Will a resistor in series (70-100R) before the rectifier solve the problem? Is this needed /important ?
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Old 9th October 2020, 10:21 AM   #839
mctavish is offline mctavish  Austria
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The series resistance is important to limit the inrush current of the rectifier tube. Without the proper resistance the tube could arc over and cause problems. I normally use 2 resistors in the HV leads before the rectifier.
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Old 9th October 2020, 10:22 AM   #840
mctavish is offline mctavish  Austria
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If the 2 halves of the hv winding have different resistances you can adjust the value of series resistance so that both halves have the same dc resistance. This helps reduce hummmmm.
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