DIY 845 Tube Amp

by mthoi Tue Jul 26, 2011 2:59 pm

Hi, anyone out there with a DIY 845 to share and compare notes on their build? Pls PM me. Tx

by mthoi Thu Aug 04, 2011 11:45 am

Seems like DIY 845s are rare projects. I am still keen to meet-up with 845 owners - Pls PM or email at mthoi@streamyx.com

Anyway, I have finalised my design & schematics and have one monoblock wired and is undergoing voltage testing. I have decided on a 12AT7/45 driving a 845 transmission tube operating at 940VDC in SE. That should produce around 15Watts of Class A.

I have plugged-in an tested the operating voltages for 12AT7 and 45 tubes and they are all within design specs. Next step is to plug-in the 845 tube and test its operating voltages before I hook up to my test speakers.

The biggest question is - Would it work and how would it sound?

I should have a busy and exiting weekend ahead. Will update with pics later.

by dixchen Thu Aug 04, 2011 12:54 pm

It would work just fine, I have a 6sn7/45 driving an 845 operating at about 450VDC that sounds excellent dissipating about 5W at Class A.

The 45 is a perfect driver for the 845 tube.

It would work fine if you are looking at running the amp without a linestage in front of it, I personally prefer the sound of octal tubes 6sn series tubes for the input.

12AT7's are not known to be nice sounding except the very rare long plate Telefunken 5965 electrical equivalents, the rest are really mediocre sounding to my ears.

Good luck..

by mthoi Thu Aug 04, 2011 2:59 pm

Good man Dixchen. Finally someone with an 845 amp - even better since it is 45/845 tube amp! When I am ready, I would arrange for an audition of the 845 amps.

I am OK with 6SN7 and 6J7s. They sounded good. Since I have not done any project in SRPP and using 12AT7 was easy since I have a pair of NOS Telefunken ECC801S diamonds. They have very good reviews.

But for testing, I have a pair of Telefunken ECC81s and Union National 45s to make sure that things are working before I do tube-rolling.

by dixchen Thu Aug 04, 2011 5:06 pm

Ah so you're running an SRPP input stage, direct coupled to your 45 I presume?

by mthoi Fri Aug 05, 2011 1:20 am

Dixchen - yes, using direct coupled.

I was sleepless and decided to work on the amp - just got it working and is playing classical music on a RM30 pasar rd speakers. I thought it sounded "good". Need some more testing and burn-in before I hook-up to my Harbeth p3es for more serious listening.

Then work on the other monoblock.

by dixchen Fri Aug 05, 2011 12:11 pm

I have no doubts it will sound good since the driver tube predominates the sound of any tube amps in this case using the 45 is an excellent choice. Besides, the 845's character is really like a big 45 tube but in my application, I prefer the more delicate and mellow character of using 450V for its B+ and besides that 5W is plenty for my application.

If I had a choice I would prefer one based on the mighty 211 tube in 1200V mains but really don't have time to build something like that la... too many amps to listen to, not enough time.. Mad

by sss333 Fri Aug 05, 2011 12:40 pm

At last all those tube DIY guy will met up ah..ha....Dixchen & Hoi in case u both meet up for any audition session just let me know lah i might wish to join to listen to 845.

Unluckily my alnico 12" still no news at all, still waiting to reach 15pair...i guess.

by noodle88 Fri Aug 05, 2011 12:53 pm

Yes, 45 can be a very good driver tube but can it be enough current to drive the 845 into full clipping? I think the b+ for 845 at 1200v will give u more juice. If I were u mthoi, I'll be using a 300b to drive the 845.

Cheers,

by dixchen Fri Aug 05, 2011 2:38 pm

Hey noodle

If you look at the specification sheets for both 45 or even the 2A3 ( nothing coming in between these two tubes that are cousins ) there is plenty of current to drive the 845, rather easily.

300B expensive leh.. 45 is much cheaper and better sounding la...

by dixchen Fri Aug 05, 2011 2:44 pm

sss333 wrote:At last all those tube DIY guy will met up ah..ha....Dixchen & Hoi in case u both meet up for any audition session just let me know lah i might wish to join to listen to 845.

Unluckily my alnico 12" still no news at all, still waiting to reach 15pair...i guess.

IF can spare the time will meet up la, my son keeping me busy all the time leh Razz

Guess you gotta be patient about the Alnico 12 la, but after putting in over 250 hours...I've got to tell you that this is a point of no return Laughing

by noodle88 Fri Aug 05, 2011 2:52 pm

Dixchen, 45 is giving out 30+ mA but 2a3 can give 60+mA leh.
Yes 45 is a better tube, the EML 45 will anytime bet the KR2a3 in my preamp. With nos 45 even better sounding. But 845 really need high voltage n current swing to drive or else u will not get the juice out of it.

by brabusm Fri Aug 05, 2011 10:06 pm

noodle88 wrote:Yes, 45 can be a very good driver tube but can it be enough current to drive the 845 into full clipping? I think the b+ for 845 at 1200v will give u more juice. If I were u mthoi, I'll be using a 300b to drive the 845.

Cheers,

Good choice. I prefer the lush 300B to the feathery 45 to drive 845. Mine was an overkill with a pair of WE 300Bs driving another pair of RCA 845s.

by dixchen Fri Aug 05, 2011 11:15 pm

noodle88 wrote:Dixchen, 45 is giving out 30+ mA but 2a3 can give 60+mA leh.
Yes 45 is a better tube, the EML 45 will anytime bet the KR2a3 in my preamp. With nos 45 even better sounding. But 845 really need high voltage n current swing to drive or else u will not get the juice out of it.

Well agreed but it all depends if you want it to be musical or you want grunt out of it la, for ex. an EML 45 used as a driver could well drive the 845 hard enough given that its operating current could be driven harder.. but the type of sound it outputs would be very different compared to say for ex a nos ST type 45 la..

Like I mentioned above, I'm listening to the ' mellow ' side of the 845 tube, ( 450V B+ ) many do not realize that the 845 can be a bit of a Jekyl and Hyde kinda tube Twisted Evil

Similarly I prefer the sound of a 45 over 2A3 any time la.. then again whether it carries out its duties as a driver or output tube, different results for sure..

I tend to prefer less ' grunty ' kind of sound these days...

The Shuguang 300B-Z could well be an exception, any other 300B's... err I have to reserve my comments le.. Rolling Eyes

Hey your new toy looks great there.. whats the driver driving the 300B la.. Shocked

by brabusm Fri Aug 05, 2011 11:42 pm

Between the 45 and 2A3, I too prefer the 45. The 2A3 sounds much more stressed relatively. Interestingly, the 2A3 is two 45s in one tube Smile

dixchen wrote:
noodle88 wrote:Dixchen, 45 is giving out 30+ mA but 2a3 can give 60+mA leh.
Yes 45 is a better tube, the EML 45 will anytime bet the KR2a3 in my preamp. With nos 45 even better sounding. But 845 really need high voltage n current swing to drive or else u will not get the juice out of it.

Well agreed but it all depends if you want it to be musical or you want grunt out of it la, for ex. an EML 45 used as a driver could well drive the 845 hard enough given that its operating current could be driven harder.. but the type of sound it outputs would be very different compared to say for ex a nos ST type 45 la..

Like I mentioned above, I'm listening to the ' mellow ' side of the 845 tube, ( 450V B+ ) many do not realize that the 845 can be a bit of a Jekyl and Hyde kinda tube

Similarly I prefer the sound of a 45 over 2A3 any time la.. then again whether it carries out its duties as a driver or output tube, different results for sure..

I tend to prefer less ' grunty ' kind of sound these days...

The Shuguang 300B-Z could well be an exception, any other 300B's... err I have to reserve my comments le..

Hey your new toy looks great there.. whats the driver driving the 300B la..

by noodle88 Sat Aug 06, 2011 9:39 am

Dixchen,

Currently I'm using a nos 45 as driver for my 300B, But the EML 45 did have much better drive compare to the NOS. But the EML don't have the delicacy of the NOS. Have u tried EML Globe Type 45 before? I might go back to KR 2A3. As the 2A3 have more reserved power compare to a 45. In my case, a KR2A3 drive the NC20 Interstage far better than any other 45 tubes.

Brabusm,

Yes, 300b as driver for your 845 is what u need. 300B will give a full swing for ur 845. If u have 1200v on the plate of ur 845, then u will get the full potential of the 845. U may need to try Shughang 300b-z?

Cheers,

by dixchen Sat Aug 06, 2011 10:05 am

Globe EML 45's? No cause of what I've read there are far too many failures of the globe tubes and besides, the drive will be even less wiith those, supposingly more delicacy but like you have heard yourself, I still prefer NOS 45's especially good Globe 45's.
I asked earlier because a friend of mine has the same setup as yours that is a 45 drive 300b but not using interstage trans la, RC coupled. 6J5 input. Would be interesting to see how different both different topology sounds side by side.

by mthoi Sat Aug 06, 2011 11:57 am

Wah - lots of 845 owners also. We should all organise a tube amp club soon.

SSWong - I would definitely invite you and rest for a listening when I get the other monoblocks completed and tested. I think if I take of the Hari Raya week, I should be able to get everything set-up.

I always think the choice of driver tubes are to your own taste - heck, also the operating voltages, pre-amp tubes, driver tubes and power tubes for that matter, would have its own signature. Also the passive components, OPT, etc..

Enjoying the music seems to be the universal theme. Of course, DIY "boys" like to play with tubes...

by mthoi Wed Aug 10, 2011 10:22 pm

I was busy-beaver over the last 2 nights and got both the monoblocks assembled and tested. They are connected to my test Coral 6B flat horn speakers - and they can play loud and clear. Soundstaging is huge even with the coral!

I personally think it is a winner over my WE91a 300b!

Anyone wishes to do a DIY 845? PM me and I would pass you all my schematics, layout and provide you with an audition of the end-result also.

How do you post pics?

by cmboy Wed Aug 10, 2011 10:40 pm

mthoi wrote:Enjoying the music seems to be the universal theme. Of course, DIY "boys" like to play with tubes...

Really? I only know it only started again in the last decade when tubes became a very popular choice for amplification again after solid state ruled firmly for at least 2 and half decades since it faded away in the mid 70's. I've never heard anyone talk or discuss passionately about tubes from 1980's to around year 2000+. Twisted Evil

by dixchen Thu Aug 11, 2011 1:22 am

mthoi wrote:I was busy-beaver over the last 2 nights and got both the monoblocks assembled and tested. They are connected to my test Coral 6B flat horn speakers - and they can play loud and clear. Soundstaging is huge even with the coral!

I personally think it is a winner over my WE91a 300b!

Anyone wishes to do a DIY 845? PM me and I would pass you all my schematics, layout and provide you with an audition of the end-result also.

How do you post pics?

Congrats, its a great moment always for a DIY'er to fire up his new engine! Laughing

Under the list of toolbars click on ' Host and image ' and click browse to select the image file from whichever directory you saved it, then click on host image, and select from the middle row ' Image ' , click copy on the right hand side, and paste it inside here and a link to the file will appear.

Winner over the WE91A huh, yours using the 310A driver or the 6C6?

What OPT have you got on it at the moment? ( the 845)

by mthoi Thu Aug 11, 2011 11:47 am

Hi Dixchen, Tx for the instructions to upload pics. Hopefully, I get it done correctly.

The WE91 uses Philips Jan 6J7. I was bidding for a pair of WE 310A on ebay but was unsuccessful. Just settled for the next most affordable pentode. I am using a Shuguang 300b-Z. Good clarity.

The 845 uses Hashimoto 10K OPT and I am using Shuguang PSVANE 845-T tubes. I think the 845 has shorter burn-in period since they sounds very good after 20+ hours.

DIY 845 Tube Amp Dsc_0112

by dixchen Thu Aug 11, 2011 1:42 pm

HI Mthoi

Excellent choice on the Hashimoto's, am using those as well for my 45 amp and also my upcoming project.

Did you know that the Russian Svetlana 10J12S built in the 1960's is the equivalent to the 310A and sounds in fact better than the American version, am using those now and they are cheap and plentiful on e bay. Great choice on the Shuguang,s, am using those as well. Prefer them over all the others including the WE's.

Plenty of Solen and AEON's there I see for the filtering stage and bypass huh, but I personally prefer ASC's and Jensen 4 poles in my build, the naturality of these are second to none.

Wonder how those PSVANE tubes sound , am using the now NOS SUPER TNT 845M's made in the 90's, no longer available now.

Love to audition your system there one day, if I get the chance la..

Great work by the way!! nice and neatly arranged.

by mthoi Thu Aug 11, 2011 2:12 pm

Tx. I will give the russian tubes a try sometime.

I got the Hashimoto from a diy-er at a discount - so no complain.

The main power section is not shown. I am using a combination of BHC and Jensen electrolytes with more solen film caps for filtering. I am slightly "new school" (Nelson Pass like huge CRC/CLC power supply in his Pass SE designs) in using large value electrolytes with film bypass - seems to work well. And space is a bit premium in this build. I have used Obbligato film oil in previous build - they are OK. I personally think film oil vs large value audio quality electrolytes are quite close.

The AEON film caps are used in the voltage bridge for the 12at7 and for cathode bypass. The solen are for power filtering.

For by-pass, I am using Mundorf Silver Gold Oil which does not show up well in the pics.

PM me if you are keen to get together.

by mthoi Tue Jun 25, 2013 3:32 pm

I have been revisiting my earlier DIY projects and started to changethe operating voltage and component values. (Since my wife have outlawed me from building anymore tube amps to clutter-up the house).

After listening to the system for nearly 2 years, I have updated the following :-
i. Upgraded PSU caps
ii. Added CLC stage for the preamp/driver circuit (12AT7 and 45)
iii. Increased the operating point from 940vDC to 1120VDC B+ supply.
iv. Changed the cathode resistors
v. driver tube rolling, finally settled on EML 45 Globe (over Acturus 45, RCA 2A3).

I can now appreciate for the need to operate the 845 transmission tubes at higher voltage - increased spaciousness and clarity.

Anyone keen to start a DIY tube amp project and require assistance?

by noodle88 Tue Jun 25, 2013 4:23 pm

mthoi wrote:v. driver tube rolling, finally settled on EML 45 Globe (over Acturus 45, RCA 2A3).

Have you tried the UX-245/345 globe before? They sound promising.

Anyone keen to start a DIY tube amp project and require assistance?

I think of making a 211 power amp after my 71a project, may need to get some idea from you.

Cheers,
cheah

by mthoi Tue Jun 25, 2013 5:26 pm

Hi Cheah,

There are great similarity between 211 and 845 - perhaps the 211 are easier to drive (cf 845), Z for 211 OPT primary is 10K.
I have a few Sound Practice article & schematics, they are all duplicated in the internet.

Looking forward to opportunity to get together on this project.

by noodle88 Tue Jun 25, 2013 6:51 pm

Hi Mthoi,

I just managed to order a pair Tango X10SF and one pair NC20F from EIFL before Tango close down. Will use them for my 211 project.

Looking forward to meet up for Hifi talk. Send you a PM.

Cheers,
Cheah

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