DIY Audio Projects Forum
http://diyaudioprojects.com/Forum/

6EM7 power amp
http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=3513
Page 19 of 25

Author:  mwhouston [ 24 Oct 2013, 18:21 ]
Post subject:  Re: 6EM7 power amp

In Australia we are just coming into our summer and we have out of control bush fires just 12 hours drive north of me and it hailed heavy here just a day ago. The weather has not allowed me to get out and sand and prime the drilled top plate for the new amp (Abstinence). This morning I got my break and either tonight or tomorrow the top coat will go on.

I have been little distracted by the thought of a tube headphone amp. Once the top coat goes on I can't touch the plate for about 4 or 5 days. This will allow time to collect the remainder of parts for this amp and possibly experiment with some tube HP amp ideas. I'm even thinking EL84. I have quite a collection of quality NOS. The thought of a UL tube HP amp with only transformer coupling excites me. Yes I should get out more.

Author:  mwhouston [ 25 Oct 2013, 18:19 ]
Post subject:  Re: 6EM7 power amp

Top and bottom plate top coated. Now to prepare and varnish the wooden Murbue base.
Attachment:
Plates.jpg

Author:  mwhouston [ 27 Oct 2013, 18:42 ]
Post subject:  Re: 6EM7 power amp

The weather improved for an afternoon allowing me to sand and varnish the base with a polyurethane spray. Nice to work with and quick drying. The wood in the base is a little rough and the varnish hides nothing. But this just adds to that home made look. This one will really look like your uncle Bob made it.

For the last of my 6EM7 amps I wanted to use some different caps. I had nothing different than I have used before in a 0.033uf size. Once more trolling eBay for some gems to pop up I found some Russian Teflon caps. Quite cheap 8 for $10. It will be a week or so before I need them hopefully they will arrive before then. I have never used these before but have read where Teflon is meant to be the dialectic to die for.

With different OPTs and other bypass caps I haven't used before plus using the Sylvania tubes this amp should have a different tone to the others. Images of the base to follow.

Author:  mwhouston [ 28 Oct 2013, 18:36 ]
Post subject:  Re: 6EM7 power amp

Image of the base and top plates. The base is dry but the plates, a few more days to go. I found something different for the amp to give it a different of look and different sound. Images to follow.
Attachment:
Base and plates.jpg
Attachment:
Base and PlatesII.jpg

Author:  mwhouston [ 01 Nov 2013, 23:52 ]
Post subject:  Re: 6EM7 power amp

Abstinence is assembled but not wired. Top plate is not screwed down. The power tranni and choke are shock mounted top and bottom to help control vibration of the top plate. This would feed directly into the tubes. I accidentally installed a 20H choke and not a 10H. Amp should be quiet!! OPTs will reside under the bonnet. Tubes are Sovteck 5Y3 (may change) and Sylvania NOS 6EM7. The amp sits on three heavy duty gold plated (solid brass) cones. These are well hidden making it like the amp is floating. Put this together in 1:20hr the fastest yet.
Attachment:
Assembled.jpg
Attachment:
AssembledIII.jpg
Attachment:
AssembledIV.jpg
Attachment:
AssembledV.jpg
Attachment:
AssembledVI.jpg
Attachment:
Isolation.jpg

Author:  mwhouston [ 03 Nov 2013, 23:26 ]
Post subject:  Re: 6EM7 power amp

It lives and went first time. I used a 6uf motor start as the first cap because I wanted to use a Sohpia Electric Prinses 5U4 equiv (274-$162). But it started sparking so back to the 5Y3. Amp is dead quiet and plays nicely just need 50 hours on the clock. Also I hoping to have some 0.033 Russian teflons but they didn't arrive so I have just tacked in some orange drops. When the new caps arrive I'll pop them in. The Chinese 15W OPTs sound OK but need lots more time.
Attachment:
underneath.jpg
Attachment:
Abstinence.jpg

Author:  azazello [ 04 Nov 2013, 02:59 ]
Post subject:  Re: 6EM7 power amp

Maybe I'm not right, but I see 1.5 kohm ceramic resistors....are they cathode resistors, it seem shunted with 100uF? If "yes" I'm afraid it is not very good choice for good sounding. Cathode resistor is more important part for sound - /In my SE 2A3, SE 6S4S, OTL 6AS7G-4 cathode load resistors I use Mills, expensive, but with high quality resistors.../. Sorry, if I didn't understand Your schematic....

Author:  mwhouston [ 04 Nov 2013, 03:21 ]
Post subject:  Re: 6EM7 power amp

azazello wrote:
Maybe I'm not right, but I see 1.5 kohm ceramic resistors....are they cathode resistors, it seem shunted with 100uF? If "yes" I'm afraid it is not very good choice for good sounding. Cathode resistor is more important part for sound - /In my SE 2A3, SE 6S4S, OTL 6AS7G-4 cathode load resistors I use Mills, expensive, but with high quality resistors.../. Sorry, if I didn't understand Your schematic....

Matt's design he has stipulated 750ohms for Rk I can't get that exact value so two 1.5K in parallel gives me 750ohms. The 100uf is the correct value and I use NP caps here for what I think is better performance.

I have some Russian PIO 4uf caps coming. These may allow me to use the expensive Sophia rec. tubes. I may also try two 6uf motor starts in series for 3uf so I can use these gorgeous rec tubes.

Author:  azazello [ 04 Nov 2013, 03:27 ]
Post subject:  Re: 6EM7 power amp

Sorry, but I mean ceramic type of resistor....type is not good choice, IMO...

Author:  Geek [ 04 Nov 2013, 04:00 ]
Post subject:  Re: 6EM7 power amp

Ceramic resistors can include the metal-oxide types, which are excellent sounding..... like the Yageo SQP or NSP types :D

They're also inexpensive.

Cheers!

Page 19 of 25 All times are UTC - 6 hours [ DST ]
Powered by phpBB® Forum Software © phpBB Group
http://www.phpbb.com/