DIY Audio Projects Forum
 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

DIY Audio Projects Forum

Welcome to the DIY Audio Projects Message Forum. Use these forums to discuss Hi-Fi audio and to share your DIY Audio Projects. Registration is free and required to post messages and view the file attachments. Registration will only take a minute and registered users do not see any advertisements. After you have completed the online registration process, check your email (including spam/junk folder) for the verification email to activate your account. New members are under moderation - so your posts will not be visible until approved by a moderator. See the Read Me 1st, Forum RULES and Forum FAQ to get started on the forum.

It is currently 21 Apr 2021, 06:19

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 9 posts ] 
Author Message
PostPosted: 22 Dec 2020, 11:02 
Offline

Joined: 15 Feb 2020, 18:53
Posts: 25
I am planning to build this project:

http://diyaudioprojects.com/Tubes/300B-SET-Amplifier/

But as a pair of monoblocks. I did not see a thread dedicated to that project but please let me know if I should be asking these questions elsewhere. Otherwise, I will let this thread serve as a log of my build (unless someone talks me out of it).

My only two questions at this point are:

Can I leave the volume pots out? It was recently brought to my attention that the presence of a volume pot in a circuit is more complicated than my simplistic notion that it simply dumps some signal to the ground (and that, therefore if a pot is at 100% its like it doesn't exist). But I prefer monoblocks without volume controls.

Second, I was having a difficult time sourcing chokes for L2 but found these:

https://www.ebay.com/itm/200H-anode-pla ... 2749.l2649

They seem right except that the rating is 35ma not 40ma. Will that be a problem? I don't have the skills to calculate the current here.

Thanks for any input, as always.


Top
 Profile  
 
PostPosted: 22 Dec 2020, 13:43 
Offline
User avatar

Joined: 03 Jun 2020, 11:06
Posts: 118
Location: France
Hi @Minarai,

I built a pair of 300B compact mono-block amps in 2015 :

Image

The schematic I designed is certainly different from what you may expect, but it works fine and flawlessly :

Image

Image

It offers two output power settings : 4W and 8W

Image

As you can see, I do not use any integrated volume pot inside these amps. For adjusting volume, I use the remote volume control of the source, or a "Potar Box" like below :

Image

I don't know how much current you expect to draw from your 300B, but IMHO a 100mA choke is a minimum.

Let me know if I can help... ;)

Cheers,

-tbln.

_________________
https://guilhemamplification.jimdofree.com/


Top
 Profile  
 
PostPosted: 23 Dec 2020, 10:35 
Offline

Joined: 15 Feb 2020, 18:53
Posts: 25
Thanks, for the response. Maybe I'll build your design someday, I'm sure its good too (though I tried to find that power transformer and could not).

But anyway, I already have OPTs and PTs that match the circuit I listed. And I've built the heater power sections.
So I'm really just looking for input on this project.
The 200H chokes are for the 6SN7 plates, not the 300B. they are only rated at 40ma in the original drawing. Still, I don't like to use underrated parts unless someone has done the math...


Top
 Profile  
 
PostPosted: 23 Dec 2020, 23:06 
Offline

Joined: 13 Jan 2018, 21:33
Posts: 402
Location: australia
I built one of the versions on this forum which I am vey happy with. Listen everyday if I can. Most of the time zero noise except for transformer external noise-almost microphonic, and a slight buzz that comes and goes after switch on. In the two versions I have had I haven’t used any chokes on the 6sn7 circuit. I did a search on 300b topics which you may have studied already or if not may turn up ideas. Suncalc performed wizard-like mathematics to estimate the residual noise of the filter stage design of his 2 stage 300b SET design lovingly constructed by mwhouston which is definitely worth researching. There is a 3 stage version of the circuit somewhat like an integrated 4S preamp with modified driver circuit posted in that thread which I wired up last year. I recycled some parts on hand from an earlier eBay 300b pcb with different transformers and choke sizing though so not a faithful implementation.

search.php?keywords=300b&terms=all&author=&fid%5B%5D=9&sc=1&sf=titleonly&sk=t&sd=d&sr=topics&st=0&ch=300&t=0&submit=Search

_________________
John


Top
 Profile  
 
PostPosted: 26 Dec 2020, 17:23 
Offline

Joined: 29 Jun 2016, 15:59
Posts: 82
Minarai,

If you don’t mind my asking, which OPTs and PTs are you using? Where did you get them from?
I am also considering building this amp.
Thanks,


Top
 Profile  
 
PostPosted: 29 Dec 2020, 10:17 
Offline

Joined: 15 Feb 2020, 18:53
Posts: 25
Thanks for the input John. I did read through much of the 300B design project by Matt (suncalc) and mwhouston. The filament supply I am using was borrowed from there. The main reason I chose not to follow the rest of that design is, I happen to have a pair of CXSE25-8-3k Edcor OPTs. Not expensive, as transformers go, but I certainly want to make use of them and they match the circuit posted by S. Tasos. Also, and I admit this is silly, but I have built several amps designed by suncalc (all of them good and i look forward to building more in the future) and feel like trying something from another author.

Danny, the OPTs are mentioned above. The PTs are also Edcor, XPWR149. They don't have enough 6.3v windings to build the original stereo version, but they will for monoblocks. They should arrive in the next few weeks and I will post my progress.


Top
 Profile  
 
PostPosted: 29 Dec 2020, 19:02 
Offline

Joined: 29 Jun 2016, 15:59
Posts: 82
Minarai,

Thanks.


Top
 Profile  
 
PostPosted: 30 Dec 2020, 05:53 
Offline

Joined: 13 Jan 2018, 21:33
Posts: 402
Location: australia
I recall sampleaccurate had an entertaining thread of his build of the JC Morrison circuit a few years back. He was quite complimentary about the sound. I think he went for smps for the 5v filaments.

_________________
John


Top
 Profile  
 
PostPosted: 19 Apr 2021, 10:17 
Offline

Joined: 15 Feb 2020, 18:53
Posts: 25
So I finally found time to make my chassis. Steel and aluminum. And I have started to fit all the bits and bobs in there.

The basic premise is this circuit but as monoblocks:
http://diyaudioprojects.com/Tubes/300B-SET-Amplifier/

My transformers are Edcor XPWR149 and CXSE25-8-3k.

My only questions at this point are:

I can leave off the volume pots by replacing them with 100k resistors?

And I was only able to find a 200H, 2k plate choke rated at 35mA, while to schematic calls for 40mA. Simple math says this is totally fine, but maybe there is more to calculating the current here than meets the eye?

Any advice on these two points (or anything else) would be appreciated, as always.


This post has a file attachment. Please login or register to access it. Only Registered Members may view attached files.



Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 9 posts ] 

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 26 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
DIY Tube Projects :: DIY Tube Amp Kits :: DIY Speaker Projects :: DIY Solid State Projects :: DIY IC / Op-amp Projects :: DIY Phono Projects :: DIY Cable Projects :: Hi-Fi Audio Schematics
© diyAudioProjects.com - Terms of Service - Privacy Policy