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Old 3rd June 2009, 01:54 AM   #1
skipper is offline skipper  United States
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Cool simple se build

Hey Guys,

Getting close to getting all my parts together. My Edcor OPT and PWRT have been shipped. Yeah!
A few more questions, I need to now order my tubes and a little overwhelmed so many choice. I want to use the KT88 because I've read nothing but good things from them. I was thinking of the Sovtek KT88 because they are $56/pair. Now I am thinking that I should first start up the amp with some cheeprs tube just to make sure I don't blow anything out.
So, what would be the cheapest tubes I can buy for stut up?

What about tube part numbers, is a 6L6 the same as a 6L6GC? A 5881WXT the same as just a 5881?

On the Tubelab site, under the Simple SE tube section, there is a table that list different tubes at different impedence/power. How does one read the table? The power numbers are what I should be referencing?

Also, I believe that I don't have to add the 5k pot for the volume if I plan on adding a pre-amp later?

Well that is probably enough questions. I am going to order the Auricaps .22uf 400v and tubes from AES, I hope those are the correct onec for the coupling caps.

Thanks for the input.
skipper

Edcor XSE25-8-5K OPT.
Edcor xpwr059
375-0-375 , 175 mA 50V .05A 6.3V CT 6A 5V CT 3A
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Old 3rd June 2009, 03:50 AM   #2
rknize is offline rknize  United States
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Default Re: simple se build

Quote:
Originally posted by skipper
[B]Hey Guys,

Getting close to getting all my parts together. My Edcor OPT and PWRT have been shipped. Yeah!
A few more questions, I need to now order my tubes and a little overwhelmed so many choice. I want to use the KT88 because I've read nothing but good things from them. I was thinking of the Sovtek KT88 because they are $56/pair. Now I am thinking that I should first start up the amp with some cheeprs tube just to make sure I don't blow anything out.
So, what would be the cheapest tubes I can buy for stut up?
Chinese EL34s were the cheapest i could find at the time. They are "Valve Art", but they are made by Shuguang. However if you are using a cathode resistor tuned for a KT88, you will probably kill an EL34 in short order. A cheap 6L6GC might do the trick (I can bias my JJ 6L6GCs with the "hottest" setting on my Simple SE and they can take it). The other alternative is to just get a second set of cathode resistors or to make a switchable setup.

Quote:
What about tube part numbers, is a 6L6 the same as a 6L6GC? A 5881WXT the same as just a 5881?
No and not really, respectively. The 6L6 traditionally has a ST-shaped ("coke bottle") envelope and more conservative ratings than the 6L6GC. The latter is usually in a straight-sided "GT" envelope and has higher anode dissipation and voltage ratings. The 5881 is sort of a lighter-duty 6L6.

Quote:
On the Tubelab site, under the Simple SE tube section, there is a table that list different tubes at different impedence/power. How does one read the table? The power numbers are what I should be referencing?
The tables are broken down by tube type, then by B+ voltage, then by OPT primary impedance. Then you select a cathode resistance based on how hard you want to run the tube. You can lookup the maximum plate dissipations yourself on the web, but red numbers seem to mean that you are at or over the max, orange means you are pushing them hard but are within the limits. On the far right you can see the estimated power output and the distortion characteristics of each scenario. Of course this is all a simulation, but it gives you an idea of what the trade-offs are and how they affect things.

Looks like your B+ will be in the 475V range and your OPT primary impedance is 5000 ohms.

Quote:
Also, I believe that I don't have to add the 5k pot for the volume if I plan on adding a pre-amp later?
Correct.

Quote:
Well that is probably enough questions. I am going to order the Auricaps .22uf 400v and tubes from AES, I hope those are the correct onec for the coupling caps.
They say that those caps should be rated for the full B+ voltage since they may see it at powerup before the tubes are completely warmed up. Once operating, the voltage across them is considerably less. Maybe George has an inkling if 400V is OK, but I put 600V rated ones in mine. AES doesn't carry them, but tubedepot.com does. I've been giving TubeDepot more of my business lately since they carry a wide selection of tubes and parts and their prices are generally lower than TheTubeStore and many other vendors. AES is sometimes slightly cheaper on certain things...you just have to shop around and compare each item if you want to save the most.
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Old 3rd June 2009, 08:49 AM   #3
skipper is offline skipper  United States
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Hi Russ,

Thanks for the response. I've read and followed your build pretty closely. You built a very nice looking SE.

Currently I am just using the cathode resistor that is called out in the part list 560 ohm. I see that on your build you built a selector to switch the resistor path. Do you have a part number for that selector switch?
I think I will get a pair of the cheeper 6l6GC to get the amp running and then later change to the bigger KT88. I will take a look at the SE power table to see what a 560 ohm resistor gets me for the different tubes.
I will also go with the higher voltage coupling caps.
One other thing I would really like to understand is the circuit. I would like to really understand what all the voltages and currents are through all the components. A long time ago I remember using Pspice to analyze RLC circuits in lab. I will just keep reading this forum and hope to regain some of that lost knowledge
Thanks again,
skipper
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Old 3rd June 2009, 12:55 PM   #4
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560 in r17/r27 will run those 6l6gcs pretty hot. My plates were glowing. I have basically the same build as you do.
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Old 3rd June 2009, 03:44 PM   #5
rknize is offline rknize  United States
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Quote:
Originally posted by skipper
Thanks for the response. I've read and followed your build pretty closely. You built a very nice looking SE.
Thanks!

Quote:
Currently I am just using the cathode resistor that is called out in the part list 560 ohm. I see that on your build you built a selector to switch the resistor path. Do you have a part number for that selector switch?
http://www.tubesandmore.com/scripts/...XP?item=P-H393

560 ohm should be a good middle-ground. I run my EL34s like this with 460V B+. The 6L6 I run a little hotter at 470 ohms. At least two builds recently have been able to get their 6L6s to glow with the 560 ohm. If I remember correctly, they were both Chinese 6L6s, not 6L6GCs. My JJ 6L6GCs don't start to glow until I crank them with about 340 ohms on the cathodes.

Quote:
I think I will get a pair of the cheeper 6l6GC to get the amp running and then later change to the bigger KT88. I will take a look at the SE power table to see what a 560 ohm resistor gets me for the different tubes. I will also go with the higher voltage coupling caps.
Sounds like a good plan. The resistors are fairly cheap, so it might be worth your while to pickup a pair of 680s as well, in case the cheap 6L6s don't like the 560s. KT88s will want to run hotter...470 or 430 would be a good choice.

Quote:
One other thing I would really like to understand is the circuit. I would like to really understand what all the voltages and currents are through all the components. A long time ago I remember using Pspice to analyze RLC circuits in lab. I will just keep reading this forum and hope to regain some of that lost knowledge
Aside from the CCS plate load on the input/driver stage, this is a pretty classic design. Should be able to model it fairly closely in SPICE. You can use an ideal current source on those plates if you can't find a model for the CCS.
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Old 3rd June 2009, 05:04 PM   #6
skipper is offline skipper  United States
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It looks like the 560ohm resistor will be OK but will run the 6L6GC really hot. I think I will look further into a selector switch. Just when I thought I was done ordering parts.

When you guy say "Crank it up" do you guys mean you change the cathode resistor which is fixed but you change the resistance on the input with the volume pot. Changing the input resistance will change the current through the cathode resistor thus "cranking it up".

skipper
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Old 3rd June 2009, 05:28 PM   #7
rknize is offline rknize  United States
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Yes, sorry. When I said "crank them" I meant that I was raising the bias current by lowering the value of the cathode resistor. The lower the resistance, the lower the voltage drop across it, which turns the tube on harder.
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Old 3rd June 2009, 05:30 PM   #8
pointy is offline pointy  United Kingdom
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the thing that will make the best sounding amp is if the tubes are a good match to the out-put transformer primary impedance........
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Old 3rd June 2009, 05:30 PM   #9
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If you dont want to make another order and have a radioshack near they have a selectable 2 pole 6 position rotary switch for $1 more than AES. The product number is 275-1386

Here is a link to it: CLICK
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Old 3rd June 2009, 05:40 PM   #10
rknize is offline rknize  United States
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I don't think they stock those...maybe they can order it though?
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