We was cleaning up my hard drive and guess what I have found? A Zip file containing one of the 300B amplifiers we built >10 years ago. (Our new products won't be in this format, this design and also the parts used are now leagues ahead of what is used 10 years ago.)
This 300B tube amplifier was made in around 2002-2003. It is still working fine as far as I know and is still in good shape/service.
It's a simple design using RC coupled 3 stage topology. 5687-RC-5687-RC-300B. Customer wanted it to be as simple as it can be so that all the components can be used are of audiophile quality. It is tube rectified with 5U4G, having a choke input configuration for better sound and regulation.The chokes and output transformers are from Hammond. 3 chokes are employed for excellent filtering and Left / Right channel separation.
Power transformer are locally with flux band and copper shield on the cores for absolute quietness. Filament for 300B are DC for zero hum as it is used with high efficiency vintage speakers.
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| 300B Tube Amplifier |
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| All the transformers are caged for safety and shielding. |
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| Top view - 5687 - 5687 - 300b - 300b - 5U4G |
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| It comes with separate filament + HT switches. |
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| JJ 300B + Tung Sol 5687 + RCA 5U4GB |
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| Input are just next to preamp tube for shortest signal path. |
J&K Audio Design
25/12/2013
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Hello Ken,
ReplyDeleteA Happy New Year 2014 to you and yours. May all good things come your way.
You have been covering some designs of 300Bs lately and I found a design from Andy Grove. The I am sending a PDF of the original design with URL and the upgrade a company in the UK is offering in Kit form. This unit is a stereo single-ended 300B design using a single 300B/channel and is resistor capacitor coupled.
They have an upgrade for the original I am going to including that as well.
Original: http://www.hificollective.co.uk/kits/pdf/300bseinst_icrt.pdf
Suggested upgrades: http://www.hificollective.co.uk/pdf/300bseupgcircuit.pdf
Which approach do you feel is best for our low powered SETs (2a3, 6b4g, 300BSE? A Resistor/Capacitor coupled or transformer coupled design? Which of these two approaches is better at power transfer vs damping control? (Some speakers like mine need max power and damping is not a problem...others have the opposite problem) Thanks for your insights. (Please hide my E-Mail address on either your blog or site.)
Warm regards
Ron
6b4a/2a3 or a 300BSEi is to have just two active stages. How does this design stack up?
If you look at the pictures on the website, you will not they use strips and place the resistors and caps under them to simplify handwork of the kitmaker. This amp
Regards,
Ron C
Hi Ron,
DeleteHappy New Year to you too!
Whether for low power SETs or other types of amplifiers, I would prefer transformer coupled if you can get a decent wide bandwidth interstage transformers with proven results and/or measurement data. Else, without known quality in the interstage transformer, then resistor/capacitor coupling will be choice since it is easier to get it right this way and there are plenty of good coupling capacitors out there compared to good interstage transformers.
It does not matter on the maximum power or damping of the speakers if you are referring to the pre to power coupling method. With RC or interstage coupling, both can drive the power stage to full power if designed right.
It is easier to have 2 active stages with interstage transformer since it can be configured as step-up to increase the voltage swing, perhaps 1:2, 1:3, 1:4 or etc to provide sufficient gain to drive the power stage to maximum output, provided the driver tube is capable of doing so. For RC stage, it is governed by the driver stage gain and good sounding high gain tubes are limited. So, for 2 stage design, it is easier if interstage can be used.
Your last statement truncated. Please complete it so that I understand your question.
Thanks for your comment!
Ken
Ok. I will send a picture but next year :-)
DeleteIt's 2014 already (next year). :)
Deletehttp://www.single-ended.com/2A3/archive/Trans-hut-audio.pdf
ReplyDeletehas listed a manufacturer of Transformers they claim is better than the Tangos were. I thought everyone would enjoy this
Hi,
ReplyDeleteI can't comment since I've no experience with that manufacturer. One of our users did comment that our 5K PP OPT is as good as the T-brand F-2021 he used previously. I've not used or tested F-2021 and therefore cannot comment. You're welcome to try it and prove that he's right or wrong. :)
What transformers would you suggest for a 300B project?
ReplyDeleteHi HighCtenor,
ReplyDeleteYou're welcome to read are recent article on 300B output transformer:
http://jandkaudiodesign.blogspot.com/2013/12/300b-single-ended-output-transformer.html
If you want the absolute performance, I would recommend our Precision Series OPT (comes with individual test specifications - USD$499 a pair). Please email us your requirements and outlook so that we can customize according to your needs.
- Official frequency response: ~20Hz – 30kHz +/- 0.5dB
- Target frequency response: ~5Hz - 100kHz +/- 1.5dB
- 50W core, 90mA.
- Much better specs if it is push-pull version.
You can refer to the following link for the list of our transformers:
http://jandkaudiodesign.blogspot.com/search/label/1%28d%29%20-%20Transformers
For budget users, they can consider the "Miniwatt Series":
- MX-2.5SE, MX-3SE, MX-3.5SE - U$159/pair
- Primary: 2.5K, 3K or 3.5K (UL tap included),
- 10W, 60mA.
For value for money, "Vintage Series" is the one to go for:
PX3.5SE MK2 - U$259/pair
Pri: 3.5K,
20W, 90mA.
Please do not hesitate to email us for more details. Thanks!
Rgds, Ken