The JJ spec sheet says that with a fixed bias you can go up to 100mA.
http://www.thetubestore.com/lib/thetubestore/JJ-300B.pdf
The important thing is to set the bias in a linear region for your B+ voltage
Otherwise you will have higher THD or even harmonics
http://www.thetubestore.com/lib/thetubestore/JJ-300B.pdf
The important thing is to set the bias in a linear region for your B+ voltage
Otherwise you will have higher THD or even harmonics
How did the EML one sound compared to the JJs?
Have you seen these?
VinylSavor: ELROG ER-300B, First Impressions
Have you seen these?
VinylSavor: ELROG ER-300B, First Impressions
Depends on the circuit and operating points. The JJ are great tubes.
For that incarnation I was using Tomchr's raw supply board with the recommended ClassicTone PT, maida regulator, and filament supplies patched in to a TSE board.
Hmmm... that unit is good for 500mA... but does not have a 5v tap. But since you have Tom's power and Maida board, it's not an issue.
I have George's TSE board and some parts already; for power unit I was planning to get:
http://www.classictone.net/40-18096.pdf
With 180mA rating, I should be able to bias each 300B around 80mA?
Also any suggestions on how to drop the 6.3V to 5V in a reliable way?
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I did it by modifying the PT. For me, it was simple because I use toroidal transformer as shown here.
Chasing the tube brand sound is not as productive as some builders think. The difference made by speaker quality and improved room acoustics totally trumps the tube selection in big ways. Here's a discussion on that.
There are a couple of power transformers I found with ~650v with CT and >200mA power rating, but with 6.3v rails only. If I understand correctly, 300B tubes need 5v?
300B tubes do, but the TSE does not - it uses a regulator to deliver 5VDC to the 300B, and DC rectification and a series dropping resistor to deliver 6.3VDC to the 5842 tubes.
You need a dedicated 5V winding for the rectifier tube heater, and a 6.3V winding for the rest. I believe the 6.3V winding needs a CT if you want to run 2.5V for 45/2A3 - you should verify that - it's been awhile.
You need a dedicated 5V winding for the rectifier tube heater, and a 6.3V winding for the rest. I believe the 6.3V winding needs a CT if you want to run 2.5V for 45/2A3 - you should verify that - it's been awhile.
In search of the ideal power transformer
Gentlemen,
Greetings for the New Year!
I have been looking up power transformers with higher power ratings. The ¨plug and play" options look like the Hammond 373FX and 373EX; but, prices are high, and ratings are 460mA and 345mA respectively - bit of an overkill and what my limited understanding is, because of higher current rating, these will run the circuit at voltage levels a bit higher than designed. Please correct me if I am wrong.
The other suitable choice I found (albeit at much lower price) tops out at 200 mA.
https://taweber.powweb.com/store/022798intsch.jpg
With a 200mA PT, what is the stable bias I can expect with a 300B?
Edit: There is the PT mod option referfed to by Evenharmonics, but would like to try with off the shelf solutions first.
Gentlemen,
Greetings for the New Year!
I have been looking up power transformers with higher power ratings. The ¨plug and play" options look like the Hammond 373FX and 373EX; but, prices are high, and ratings are 460mA and 345mA respectively - bit of an overkill and what my limited understanding is, because of higher current rating, these will run the circuit at voltage levels a bit higher than designed. Please correct me if I am wrong.
The other suitable choice I found (albeit at much lower price) tops out at 200 mA.
https://taweber.powweb.com/store/022798intsch.jpg
With a 200mA PT, what is the stable bias I can expect with a 300B?
Edit: There is the PT mod option referfed to by Evenharmonics, but would like to try with off the shelf solutions first.
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Hi zman 01,
Happy new year!
I see in the picture you posted that this transformer is 720v center tapped @ 200mA.
My hammond 376x is 660v center tapped @ 173mA. My B+ is 320v.
I'm guessing that you would have no problem maintaining a near 400v loaded B+ with this unit which is ideal for the tubelab SE.
Happy new year!
I see in the picture you posted that this transformer is 720v center tapped @ 200mA.
My hammond 376x is 660v center tapped @ 173mA. My B+ is 320v.
I'm guessing that you would have no problem maintaining a near 400v loaded B+ with this unit which is ideal for the tubelab SE.
jamicomon,
You are right - the picture shows it has 720v windings with CT. However, 360-0-360 is probably too high for 300B in Tubelab SE?
It also shows 660v - and there's a red/yellow wire designated as CT (likely for both 720v and 660v?)
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