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 Post subject: EL34 SE project share.
PostPosted: 23 Mar 2016, 10:26 
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I thought I would share this build.

This amp has switchable output configurations don't switch while the amp is ON power off then change over!

Just for interest. I tend to scribble a lot sorry!
The supply filter is from Rod Coleman which has an impact, but is sometimes difficult to implement.

Presented as a fun build, its been hacked and chopped at until its usable for me I was looking for a general purpose fun usable amp.
It uses a variety of tubes why? good question. :D
NB Electron stream is copy write protected even if you think its pants or not :D (not by me)

I tried a few different things and wanted something to use while watching films and listening to music.
So I ended up with a PYE-stream. LOL

I know about the capacitors in the PSU its meant to be that way. :D

I tried different CCS but went back to 317T.

Component Synergy (for those interested)
Tantalum Magnetic 0.5 Watt
22k, 1M, 10K.
Tantalum Magnetic 1 Watt
150K.
Tantalum non-magnetic 0.5 Watt
470K.
Kiwame
220 Ohm 2 Watt direct on tube socket.
Ohmite audio Gold
15 Ohm 5 Watt.

Diode on U/L 4007.

Coupling Cap
0.15uF or 0.1uF Audyn true copper.

Cathode cap is 100uF silmic

Output tubes EL34/6L6/ etc etc
Driver ECC81/82/83.
Output Tx GXSE 2.5K/8 ohm<<cathode FB. 15 Watt version.
Input wiring silver wire used with foil screening and for input to tube Grids.
Solder Audio note or Mundorf silver /gold.
NB don’t use ordinary solder with silver wire. But you already know that. :D

The cap type FKP1 is critical on the filter.

I play all sorts through it rock/pop/films/classical..etc.
Is it linear is it audiophile is it etc. Who cares?

Regards
M. Gregg


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PostPosted: 23 Mar 2016, 12:57 
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Its going back a while,

But here is the chassis build.

The tube sockets are all mounted on silicone washers and inserted into the top of the chassis.
I have spent many hours trying and retrying different combinations of circuit and components so it hasn't been arrived at without care.
The front panel was glass drilled for the volume control which is mounted on a copper support behind the panel.
It was built some time ago but has constantly been modified and tried and re-modified etc.

The CCS allows for simple plug and play of output tubes no bias set required and is modified for CFB.
Power transformer is XPWR146-240.

So there you go a shared build, just for fun!

Regards
M. Gregg


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PostPosted: 26 Mar 2016, 05:27 
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I just noticed,

On the drawing I show the heater supply with grounded centre tap an error on my part (sorry) its a CT created with two 2 Watt 220 Ohm resistors.
As can be seen each side of the lamp on the PSU picture. The picture shows Mills 3 watt in the CCS these are now replaced as quoted with Ohmite Audio Gold.
For anyone that is not familiar with the resistor CT its just two 220 ohms in series across the heater winding with the middle of the 220 ohms connected to Gnd. All heaters are twisted pair! I use silver plated solid core PTFE its got a smaller cross section for the same current capacity. The inrush suppressor for the HT (green) can be seen in series with the 6 turn ferrite (next to the large red cap which is the filter cap 22nF that works with the ferrite to create the filter). The black inrush suppressors are in series with the mains input to primary of mains TX. and have two ferrite 5 turn in series with live and neutral. Not essential you can just rely on a mains filter. Its just a bit overkill. The blue disk ceramics are across the four UF4007 for the bridge rectifier. Very basic stuff really you can use HEXfred which work really well, I tried schottky the less said the better in this position. The green 5 Watt Kiwame is the 470K discharge resistor.
The amplifier section is built in tag strip and mounted on double sided PCB as a screen. I have use RFI tape screening but its overkill.


Regards
M. Gregg


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PostPosted: 26 Mar 2016, 10:35 
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For those interested,

here are the amp section tag boards. The resistors are all tantalum magnetic except for one which is tantalum non-magnetic.
They are just mirror image left and right.
They have been soldered and de-soldered so many times I thought about a remake but they work OK so they will do.

VERY important to ensure all earth bonding is completed back to mains earth all extraneous metalwork, including transformer metalwork, chassis screening etc to ensure fault clearance of fusing in the event of a fault
Use heavy gauge wire for the earth bond on the Output Tx secondary make it mechanically strong. Also provide an Earth bond to the bottom plate of the chassis can be with a spade crimp type connection. Should anything come adrift and touch down the earthed base plate should allow fuse operation in the event of a short! More careful bonding is required with a wooden chassis remember to only bond on mounting points on transformers to be sure not to create a shorted turn by accident. (unless you know what your doing)

Remember to insulate the ferrites with heat shrink :up: .


Regards
M. Gregg


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PostPosted: 27 Mar 2016, 01:59 
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Joined: 06 Jun 2008, 18:23
Posts: 4834
Location: Australia
Your schematic of the amp or PS didn't excite me but I love your build. Love the timber chassis and the routed tube socket cutouts. I can't believe how packed it is nunder the bonnet. The finished product looks great. Have you had a listen yet?

I'm a big fan of tube rectification for tube power amps. Before the end of the year I hope to have a 6L6 up and going, another Suncalc design. But of all the power amps built my two EL34s were of the most impressive. Good work.

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Website: retro-thermionic


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PostPosted: 27 Mar 2016, 02:24 
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Thank's for the comments,

The amps been running for some time now, its been constantly modified.
Its reached a point where it does what it says on the tin so to speak.
I can just plug and play most tubes I have lying about and it sounds quite good.
I run films and all types of music through it.
I run an OTL amp as well and the EL34SE now sounds very similar.
My RH is more compact but not quite as powerful as it uses EL84/EF86 running true triode and tube rectification.
I'll post a pic so you can see.

Regards
M. Gregg


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PostPosted: 27 Mar 2016, 11:30 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi, I agree with Mark, Very nice construction I too like the wood, but IMO it is way too crowded for a tube amp. Heat is the great enemy and extra space around components is the cure. Capacitors are particularly sensitive to heat. I would use a chassis about twice the size to insure longevity. A second benefit for less crowding is there is less chance of picking up hum and noise from other nearby wires and components. It also is a lot easier to trouble shoot / fix if there are problems. I expect my designs to function for a very long time. 20 years or so seems about right before any service is necessary. BTW the earliest of my projects (a Poddwatt) is now 10 years old and still going strong (with the original tubes as well).

Good listening
Bruce

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PostPosted: 27 Mar 2016, 12:15 
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Hi Bruce,

My builds are probably biased because I worked on tube op amp industrial equipment for 30 years.
My first tube amp is 35 years old.. :)
If industrial control was built the way we like to build tube amps the factories would never have been big enough, its also good to look at hand held WW2 radio gear its an inspiration.
The SE El34 is dead silent, there is a slight magnetic pick up on the RH output Tx's because of the tight build but I was aware of it at the start.

The small RH is ducted for the heat. the EL34se is cool inside no problems, I drive the venting using the heat from the components.
The first build is all aluminium no wood, I don't see the point of building for something to last 60 years anymore technology is moving to fast but that's just me. LOL

I think the thing to remember is most old tube equipment was enclosed, if we can't build compact with the tubes sticking out the top of the chassis there is something wrong! (Different philosophy I guess) Obviously with exception for large tubes like 845/211 etc.

All the best
M. Gregg


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PostPosted: 10 Apr 2016, 06:13 
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I just noticed the NTC type is missing,

This is the one in series with the diode bridge not the mains input.

Its this:
TKS SCK-101201MS 120 Ohms 1A NTC Inrush Limiter Thermistor
http://www.rapidonline.com/electronic-c ... or-26-7613

So A on the drawing is the 6 turn ferrite in series with NTC.

The mains input is two CL60.
NB NTC not PTC..sorry..

Regards
M. Gregg

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Last edited by M. Gregg on 10 Apr 2016, 07:16, edited 7 times in total.

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PostPosted: 10 Apr 2016, 07:01 
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Thanks for sharing your build. My first thought looking at the underside was "sure is busy under there." Great job.


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