Building the Damn Good 300B

[Bill3331]

Hi Everyone,

I'm starting a thread on my build of Tom Christiansen's Damn Good 300B (DG300B). I've built amplifiers from kits before, but this is my first time building anything from circuit boards and a bill of materials. So there may be some learning curve.

My reason for building a 300B is that I'm looking for more intense tonal color than what I'm able to get from my other amplifiers. I'm hoping to end up with some of that 300B midrange magic. I did shop around quite a bit before I settled on Tom's design. There are a few reasons for going with this amp: it's well reviewed by the people who have built it, the cost of entry is low, and I'm not paying for parts I don't need. (cough *chassis* cough). I'm on a shoestring budget, so being able to get started with the circuit boards, then order the parts piecemeal, and pick up the big ticket items like the transformers and tubes a few months down the road is a big help.

This won't be an all-out attempt at highest possible sound quality - at least not right away. I'll be using the lowest cost recommended parts, partly because I'm on a budget, and partly because I'm not completely sure that the Damn Good 300B will work well with my system. Gain is the first major concern. I don't normally use a preamp, all of my amplifiers have some sort of volume control and I run them straight from the CD player or DAC. The Damn Good 300B is not a high gain design. Depending on the input tube used, it varies from 4x to 6x. This might or might not be enough gain with my speakers and room. It'll be a close run thing, I'll have to see. The other concern is output impedance. The Damn Good 300B has no negative feedback, and my experience with no NFB amplifiers in the past has been very mixed. Most often they produce a very uneven frequency response with a hump in the midbass and way too much treble. I asked Tom about it, and he says he gets a frequency response with this amp similar to his solid state amps. I don't know if this will be the case with my speakers, but I'm willing to give it a try.

So I'm a little tentative about things, but at the same time I really love a good audio project and I'm fascinated to see what the 300B will bring to my system. So I'm looking forward to this.

 

[tomchr]

Sweet! Thank you for starting a build thread. I always enjoy seeing the work of the people who build my circuits.

A bit of background information can be found in this DIY Audio thread: http://www.diyaudio.com/forums/tubes-valves/218217-deathtrap400-pretty-damn-good-300b-amp.html

Also, my DG300B website contains a bunch of design details as well: Damn Good 300B (DG300B)

~Tom

 

[Bill3331]

I've been corresponding with Tom by email since I bought the boards, so I'd like to post up some of the more informative exchanges we've had.

I originally wrote:

I've been looking through the BOM for the driver board and I don't see a
a listing for either the 300B or the noval tube sockets. Is there a
source you recommend for these items?

In the case of the 300B sockets, it looks like it is supposed to be
placed over the large holes in the driver board and then attached to the
circuit with wires, but how do I attach the socket to the board?

The footprint of the noval socket on the PCB must have been created to
match the pinout of a particular socket, but which one?

Tom replied:

The tube sockets are available from sources such as AES, VT4C, and eBay.

I bought some ceramic base sockets with gold pins for my 300Bs on eBay from some dude in Hongkong/China. The driver tube sockets, I’m pretty sure I got on eBay as well, though AES will be a good source there. AES also has the Solen caps, should you choose that option (hint: The Panasonic cap on the BOM is just as good and much less expensive).

The small sockets need to have a pin circle diameter of 0.75” (19 mm) and be for PCB mounting. The sockets go on the back side of the board. Please see the Assembly Section of the driver board page.
As you mention, the 300B sockets are mounted to the chassis and have their pins poke through the board in the two large holes. The pin connections are marked on the board: P, G, F, F for Plate/anode, Grid, and Filament (x2) respectively. I suggest orienting the socket such that the pins of the socket line up with the respective connections on the board. Have a look at the inside view of my DG300B amp near the bottom of the DG300B page. Click on the image for a larger view. In most browsers, you can click again and get an even larger view.

I originally wrote:

I am preparing to order parts for the filament regulators from Digikey,
and it looks like the following parts are not available. Can you
recommend replacements for them?

Part 445-1587-1-ND (C8 FilReg) is marked obsolete and is unavailable.
Part 609-3390-ND (JP1 FilReg) is only available in quantities of 2000.

Tom replied:

445-1358-1-ND would be a perfect replacement for C8.

You don’t need to populate JP1 on the filament regulator board. It’s an option. It can be used to synchronize multiple regulators. It should be marked as “DNP” on the BOM.

 

[Bill3331]

Tom,

I'm going through the bill of materials for the power supply and preparing my order for Digikey, and I'm running into these issues:

1 W10G-E4/51G3-ND Not in catalog
1 BC557CGOS-ND Only available in quantities of 15000

Can you give a source for these parts?

Also, what are OPT1-6 on the BOM? Does this refer to the mains transformer?

Thanks

 

[muskyhuntr]

Both the bridge rectifier and the transistor are available at Mouser. The transistor is listed as end of life. Search for w10g for the rectifier at mouser.

Me

 

[20to20]

My reason for building a 300B is that I'm looking for more intense tonal color than what I'm able to get from my other amplifiers. I'm hoping to end up with some of that 300B midrange magic. I asked Tom about it, and he says he gets a frequency response with this amp similar to his solid state amps.

If the SS amps are run of the mill then the FR will be flat which is what you want from an amp. It's not the job of the output tube itself to screw-up the signal coming to it so if you're looking for the 300B to do the work of a EQ to boost the midrange then you'll be dissappointed. An amp should be designed to give a flat FR from input to output. The 300B itself won't create your magic. If it did, everyone who wanted a flat FR from their own 300B amp would have to compensate for an unwanted midrange boost.

20

 

[Bill3331]

Ok, it looks like I can definitely get the transistor from Mouser:

BC557CG ON Semiconductor | Mouser

The bridge rectifier I'm not sure about. Since I couldn't find the given Digikey part number, I'm not certain what the manufacturer's part number is. If it's the Vishay Semiconductors W10G-E4/51, then it's available from both Digikey and Mouser. If it's not, then I'd need to do a search for the correct part. Tom?

 

[tomchr]

Pardon the long response time here. I didn't subscribe to the thread until now. If you need to get in touch with me and expect a fast response time, email is the best option. You can also use the Contact Us form on my website (which sends me an email).

BC557 is a pretty generic PNP in a TO-92 case with C-E-B connections. Mouser P/N: 512-BC557BTA. $0.22/each. Digikey P/N: BC557BTACT-ND. Same price.

The W10G is a small rectifier bridge. 1000 V, 1.5~2 A. Circular WOG footprint. The 400 V version will work just as well in this application: Vishay B250C800G-E4/51 Digikey P/N: B250C800G-E4/51GI-ND. $0.52/each. Not in stock at Mouser.

~Tom

 

[Bill3331]

Tom,

Thanks for the reply. While I'm looking at the driver BOM, which E88CC tube did you use and like? Does it matter if it's an E88CC or an ECC88? Also, is there a source for the JJ 300B tubes that you recommend? I see that they can be gotten from ebay or from a number of online retailers.

I've been looking more closely at the 9 pin tube sockets. The only 9 pin PC mount sockets I know of are the Chinese ceramic ones, the Beltons, and the Yamamotos. The Chinese ceramics and the Beltons are both 21mm pin circle diameter and the Yamamoto sockets are 11.8mm. Can you give a link to your source for sockets with the 19mm pinout?

Bill

 

[azazello]

PCC88 is driving 300B in my SE. PCC88 and ECC88 are the sames, only heating is different - PCC88 - 7 V, ECC88 - 6.3 v. Sound is amazing!

 

[Bill3331]

Azazello,

What brand tube are you using, and where did you get it?

 

[tomchr]

While I'm looking at the driver BOM, which E88CC tube did you use and like? Does it matter if it's an E88CC or an ECC88?

I think the E88CC is supposed to be a "precision" tube with lower noise. I've heard both and not noticed any difference really. I use JJ E88CC/6922 tubes. $12/ea at AES.

The PCC88 tubes are awesome. I auditioned a pair and really liked them. I forget the brand (I'm not that brand loyal, really... ) I ran the PCC88 heaters at 6.3 V rather than 7 V. They gave a really sweet sound. Definitely a classic tube sound. I think eBay, ESRC, or www.vacuumtubes.net are your friends here.

Also, is there a source for the JJ 300B tubes that you recommend?

Sure. AES = Antique Electronic Supply. $222.50/matched pair. The tubes in the DG300B don't need to be matched, but hey... it's only $2.50 extra (~1 %) for the matched pair, so why not.

I've been looking more closely at the 9 pin tube sockets. The only 9 pin PC mount sockets I know of are the Chinese ceramic ones, the Beltons, and the Yamamotos. The Chinese ceramics and the Beltons are both 21mm pin circle diameter and the Yamamoto sockets are 11.8mm. Can you give a link to your source for sockets with the 19mm pinout?

That's a bit surprising. I forget if I bought mine on eBay (either from China or from a vendor in Portland, OR) or from ESRC. I'm thinking eBay. There is a metric ton of sockets available that will fit the PCB. Just search for "ceramic tube socket 9-pin pcb" and you shall find. It looks like some are 20 mm pin circle diameter. Others are 18 mm. Either will fit fine in my boards.

~Tom

 

[azazello]

Azazello,

What brand tube are you using, and where did you get it?

I used Tesla. I changed them with my DIYfriends or bough in DIY tube bulg. forum.

 

[Bill3331]

Okay, it's been a while but I'm ready to move forward with my build once again. To give an update on where I am, I have the boards and all the electronic parts. What I don't have yet is the transformers, the tube sockets and the small signal tubes, but I should be able to pick those up soon. In any case, I can start putting the components on the boards.

The question I have for Tom is, what voltages do I need to build the three filament regulators to? I know I knew this back when I ordered the parts, but I can't remember it nor can I find it on your web site or in the documentation I downloaded. The amp is being built with 300B tubes and PCC88s.

Also, are there instructions for how the different boards and transformers get wired together into a functioning amplifier?

Thanks!

 

[tomchr]

The question I have for Tom is, what voltages do I need to build the three filament regulators to?

You'll need two 5.0 V regulators and one 6.3 V regulator.

I know I knew this back when I ordered the parts, but I can't remember it nor can I find it on your web site or in the documentation I downloaded.

The documentation is in your email. I always send the design doc to the email address that you use with Paypal, so please check there. Should you need another copy, just toss me an email.

The amp is being built with 300B tubes and PCC88s.

Awesome. I used 6.3 V with the PCC88 tubes and really liked the results.

Also, are there instructions for how the different boards and transformers get wired together into a functioning amplifier?

Yep. That's in the DG300B Design Documentation document. It's about 30 pages and you'll find the top level hookup diagrams towards the end.

The documentation used to be on my website as the DG300B design is from the time when Neurochrome was more of a self-sustaining hobby than a business and I basically gave my designs away. Neurochrome is now my only source of income and a full-fledged business while I am retooling for my second career.

If you bought boards from me but don't have access to the documentation, just toss me an email.

Tom

 

[Bill3331]

Hi Tom,

Thanks for getting back to me so quickly. I did find the DG300B design document in my email history, so that's all good. But in looking over the documentation, I don't see any build instructions for the Maida regulator. I have a BOM and schematic, but are there any instructions on how to populate the board? Or is it pretty straight forward?

 

[tomchr]

Thanks for getting back to me so quickly. I did find the DG300B design document in my email history, so that's all good. But in looking over the documentation, I don't see any build instructions for the Maida regulator. I have a BOM and schematic, but are there any instructions on how to populate the board? Or is it pretty straight forward?

The 21st Century Maida Regulator used to just come with the schematic, BOM, and component calculator. I now have a complete design document for it. Please toss me and email and I'll get it to you.

Thanks,

Tom

 

[zman01]

Bill3331,

Good to see that you've "restarted" the build. Look forward to updates and some pics.

 

[Bill3331]

Hi everyone,

After a long hiatus, I am once again working on the DG300B amplifier. I've started soldering together the power supply board, and ended up doing a complete parts inventory to make sure I don't miss anything while I order the last few bits and pieces. One thing I'd like to do is get standoffs for the circuit boards which will allow me to suspend them above a piece of plywood. I know I've seen pictures where the filament regulator boards were stacked up on top of each other using standoffs of some kind. Something that has a screw on one end and a hole fitted to that screw on the other. Can anyone give me a part number for the standoff used?

 

[HollowState]

This type of item is made by HH Smith, now Abbatron, and comes in various lengths, shapes and thread sizes. I get some from eBay by searching "HH Smith" or "standoff'. (8200/8300 series) They also make hollow spacers to use with a long machine screw.