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Tubelab Discussion and support of Tubelab products, prototypes and experiments

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Old 25th August 2019, 04:21 AM   #1
csample is offline csample  United States
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Help Needed with TSE-II Configuration Decisions for a First Time Tube Builder
Default Help Needed with TSE-II Configuration Decisions for a First Time Tube Builder

I am building my first tube amp and would really appreciate help from experienced builders to select the right configuration and parts for a good outcome on my TSE-II build.

Background Information

Before I jump into the build decisions, I wanted to provide some details on my system, musical tastes, and goals for the amp.

My primary speakers are Wooden Designs Vulcans (FE206EN Back Horn ~ 96 db efficency) they make good bass and I would like to run them full range with this amp. In another thread there was a comment that the impedance of these speakers might be a problem for a tube amp. I have included a simulated impedance chart below taken from this thread. Does the impedance look ok?

I mostly listen to classical/acoustic music and classic rock, at moderate volumes (usually at night when the kids are in bed).

I have two goals for this amp 1) to get an accurate feeling for what a very good tube amp sounds like 2) make the amp versatile enough to run both high efficency drivers and some thing more conventional along the lines of Lynn Olsen's Ariel speakers.

If I am really missing the boat on my build decisions, please keep in mind that I have never heard any tube amplifier before, and never even held a vacuum tube until my 5842's arrived a couple days ago.

Build Decisions:

Tubes: 300B's - Available New, Most Power (helps with the versatility goal), Good Reputation, thinking Genalex Gold Lion from Viva Tubes (~$210 per pair)

Output Transformer - 5000 ohm primary, Multitap 8 ohm and 4ohm. Based on the Western Electric table of "Recommended Operating Conditions" for the 300B i am thinking that a 5000 ohm primary operating around 400V and 60 mA would be a good balance of power vs. distortion. Thinking the One Electron UBT-2 would be a good choice, but I am definitely open to something else.

Built in Volume Control - I would like to include a built in volume control and source selector, but I don't know the gain of this amp. Any idea on the gain of a 300B TSE-II?

Thanks!
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Old 25th August 2019, 05:05 AM   #2
evanc is offline evanc  United States
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Help Needed with TSE-II Configuration Decisions for a First Time Tube Builder
Electra-Print.com Audio Transformers
You might consider electraprint output transformers.

I have a pair of ariels they sound very nice driven by my TSE with 45 output tubes. Obviously no rock concert volume.
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Old 27th August 2019, 04:54 AM   #3
csample is offline csample  United States
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Help Needed with TSE-II Configuration Decisions for a First Time Tube Builder
Hi Ė I think my original post was a bit too wordy and vague. Hopefully it didnít leave anyone permanently confused. What I am really looking for is confirmation that I am heading in the right direction before I buy parts.

How does the following list look for a TSE-II amp that runs only 300B tubes?

Tubes:
Genalex Reissue 300B
Genalex 5AR4 Rectifer
Raytheon 5842

Power Transformer:

Edcor XPWR178, 660V 200mA center tapped, 6.3V 6A center tapped, 5V 3Acenter tapped

Choke:

Edcor CXC150-10H-300MA, 10H 300mA, 72 ohm DCR

Output Transformer:

Electra-Print, 4K primary, 6 ohm secondary, 100mA

With the 6 ohm output I am thinking that I would be able to create the following conditions:

With 8 ohm load transformer acts like 5333 ohm primary (8/6*4000ohm = 5333 ohm)
With 4 ohm load transformer acts like 2664 ohm primary(4/6*4000 ohm = 2664 ohm)


Suggested operating conditions for each primary resistance from the WE300B recommended operating conditions table are:

~5000 ohm 400V Plate, -87 V Grid, 60mA Plate
~2500 ohm 400V Plate, -84 V Grid, 80mA Plate

Anybody see any red flags, or am I ok to start purchasing these components?
Suggestions?

Thanks!
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Old 29th August 2019, 01:36 AM   #4
csample is offline csample  United States
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Help Needed with TSE-II Configuration Decisions for a First Time Tube Builder
Jack at Electra-Print was very helpful in choosing a set of output transformers. They will be 5000 ohm primary, 6 ohm secondary, 100 mA. Biggest question in my mind now is the choke. Will the 72 ohm resistance of the Edcor 10H 300mA choke cause the B+ voltage to be too high? I am shooting for ~400V.

Also, any suggestions on which cheap set of 300B tubes to use for intial start up and adjustment? Can the Sovtek 6A3 be substituted?

Thanks!
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Old 30th August 2019, 03:12 PM   #5
zman01 is offline zman01  Bangladesh
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Help Needed with TSE-II Configuration Decisions for a First Time Tube Builder
csample,

400V might be too high anyways... though some folks do run their 300B at such high B+ . With your power transformer and choke, probably you will get around 370V with ~70-75mA bias for the 300B tubes. This estimate is mostly from memory from playing around with the Tubelab SE (no longer in service). The recommended operating points in the WE 300B are of course valid, but other points will also work - so be ready to be flexible within the limits.

I recall George recommending the Sovtek 5AR4 as a robust rectifier tube - I have used them, found them reliable till date.

Last edited by zman01; 30th August 2019 at 03:15 PM.
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Old 30th August 2019, 04:44 PM   #6
Andrewbee is offline Andrewbee  Jamaica
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csample,

As Zman01 says, with that 660 CT you are looking at approximately 370 - 380 Vdc B+. ( My rule of thumb is half the CT voltage times 1.15 - e.g. 330Vdc*1.15= 379Vdc.)

You can vary the first capacitor in the CLC B+ supply to "tune" the voltage by a few volts. Choke D.C.R. will also play a part in B+ voltage so there are many variables.

Your choke at 300mA is large, you could go smaller.

I would not use 400 volts B+. Its on the high side and some 300B's may not take it well.

I have used both JJ 5AR4 and a Chinese 5AR4 and got ~ 10Vdc more B+ using the JJ tube with same wall voltage (122 Vac) so more variables.

Look at the W.E. 300B specification sheet for recommended operating points.

I use a Hammond 600 VCT 300 series P.T. with a CL90 I.C.L. and Hammond 10H 200mA Choke (still a bit big) and end up with exactly 350Vdc B+ with 300B's running at 50mA/5K which according to the the spec sheet gives 6 Watts output, the 300B's running at 17W

imho I don't see the point in running the output tubes to the 9 -10 Watt level.
I suppose the plate resistance goes down as does the distortion at the expensive of longevity but I feel the sq goes down as well. I doubt you would detect a volume increase either.
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Last edited by Andrewbee; 30th August 2019 at 04:53 PM.
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Old 31st August 2019, 12:52 AM   #7
csample is offline csample  United States
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Help Needed with TSE-II Configuration Decisions for a First Time Tube Builder
Zman01 and AndrewBee, thanks for your thoughtful and detailed replies. The real life B+ voltages for a given transformer, choke, rectifier are very helpful, I tried to calculate the power supply voltage, but it just got to complicated.

I was choosing the ~400V B+ voltage based on the lower distortion numbers in the WE 300B charts and based on George's preference for it in his 300B SE amp. However, as you point out, I really can live with lower power levels, so I will spend some time looking over the performance data at ~350v this weekend so see if I can weigh out which B+ voltage I want to target.

Chas
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Old 31st August 2019, 02:47 AM   #8
zman01 is offline zman01  Bangladesh
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Help Needed with TSE-II Configuration Decisions for a First Time Tube Builder
Chas,

IIRC George prefers a 5K transformer but runs his tubes around 360V B+ and 60mA bias?

Have you ordered the OPT from Electraprint? Does Jack to dual-secondaries? If yes, then I would suggest both 8 Ohms and 16 Ohms secondaries. With your 5K OPT, connecting 8 Ohms speakers to the 16 Ohms tap would result in the tube seeing a 2.5K load.

Then you could listen and decide which one you prefer more - lower distortion and higher damping factor with 5K load line, or slightly more distortion and lower damping factor with 2.5K. There is no right or wrong in which one you prefer.
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Old 31st August 2019, 03:34 AM   #9
zman01 is offline zman01  Bangladesh
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Help Needed with TSE-II Configuration Decisions for a First Time Tube Builder
Regarding the choke, if you are willing to put it underneath the chassis, you can take a look at the Triad-C14X or even the Triad-C17X.

The C14-X has a DCR of 150 ohms, so voltage drop will be more. The C-17X is only 1.5H but much lower DCR of 40 Ohms - but George has used it and did not get any hum on his build:

After a 14 year run, the TSE must DIE!
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Old 1st September 2019, 05:15 AM   #10
csample is offline csample  United States
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Help Needed with TSE-II Configuration Decisions for a First Time Tube Builder
After reading this thread Why the wimpy 300B operating points? I have decided to go with the higher voltage (390) and current (90-100mA) operating point capable power supply. I ordered the Edcor XPWR278 transformer (660 V Center Tapped, 325mA) thinking that the larger transformer will help supply surge currents for transient demands and that it might also help reduce transformer mechanical noise. I did some filter calcs (hope I got them right) and targeting a -90 dB ripple voltage I should need ~ 4H on the choke. I ordered the Edcor CXC125-5H-300mA because I wanted to avoid saturating a smaller (200mA) choke if I am running nearly 200ma total plate current.

Now I need to start thinking about what type of enclosure and physical layout to make. I really like the beautiful wooden framed amps I have seen in the Tubelab picture thread, and I am inclined to go this route, but I am concerned about covering the tubes for safety reasons. Anyone know of commercially available tube cages that would protect the tubes, but not totally change the look of the amp, like a full cover would?

Thanks again!
Chas
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