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Old 16th May 2011, 1:28 pm   #61
tri-comp
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Default Re: 2C34 Project taking off...

More progress...

The second amp was wired and caused me all kinds of problems with self-oscillation when the NFB was connected.
NOT the 'Switched-Anodes problem' as that gives a clearly audible oscillation; this osc-freq. was around 60KHz and the reason couldn't be found w/o a scope.

Today I finally had a chance to work with a scope and to see what goes on with the oscillation.
As I couldn't find any wrong wiring or component-values etc. I suspected something could be wrong with the OPT.
Oh, how wrong I was.
When you have to work in the blind w/o access to even a scope it's next to impossible to pin-point exactly what goes on and why.
I had adjusted the NFB for the oscillating channel by temporarily disconnecting the good channels NFB-pot and measuring the resistance-value of the pot. and setting the second channel to the exact same value.
First of all, that value was way too low. The pot was set for 1K and it was on the edge of setting the first channel oscillating just like the second. I just didn't see w/o the scope.
So, it turns out nothing was wrong with the second channel except too heavy NFB setting the channel off oscillating around 60KHz.
For now I've re-adjusted both channels for something like 5K; final valus is still an item TBD.

I measured the output Vpp with the scope and experimented with the secondary taps. Max power output is obtained with a 4-Ohm load on the 4-Ohm tap. An 8-Ohm load on this tap gives higher output that when connected to the 8-Ohm tap.
Max. undistorted output is around 16Watt/4-Ohm and 12Watt/8-Ohm.
That's not halfway bad for a 2C34/RK34 PP

The CF/CCS takes the 2C34 grid right to +20V before clipping. 2C34 g1-to-g1 = 150Vpp. Any distortion I could see on the scope hangs on the Concertina-splitter. I believe the CF/CCS is not even sweathing and will probably be applied elsewhere in the future.

I'll upload more pictures and corrected circuit-diagrams in time.
For now the Pre/Concertina is wired a rats-nest and is not suitable for display.
In a weeks time I'll have the final wiring done and more pictures available.

Huey Lewis & The News helps me celebrate..
Nice firm and full bass, clean treble, undistorted vocals and a real nice album

rgds,

/tri-comp
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Old 18th May 2011, 9:22 pm   #62
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Default Re: 2C34 Project taking off...

Getting closer to finishing the project.
I don't think I can improve much on the sound without an audio-analyzer.
Actually I'm building one at the moment but my chosen soundcard appears to be not the very best choice (Sound Blaster X-Fi HD)
When it's done I'll be able to do sweeps and spectrum analysis with a build-in 4/8 Ohm switchable stereo dummy-load
Tonight I finished (95%) one channel while the other preamp/concertina is still a rats-nest, but working.
Since I took a couple of pictures I've decided to share.
Friday is a nat'l holiday so I should have a chance to really finish all wiring.

In case you're wondering the Pioneer turn-table is playing ELO's Greatest Hits.
Huey Lewis wasn't nostalgic enough

rgds,

/tri-comp
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Old 30th May 2011, 9:01 am   #63
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Default Re: 2C34 Project taking off...

Rob,
Instead of using RK34 look for couple of CV18 or VT61. These are super version of same tube but increased current and dissipation.
Do remember Class A RMS Watts out = 20% total dissapation
15 watts music power. This tube has ceramic base too and can take 450 volts continuously.
And sound almost as nice as 300B

rgds
Keith
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Old 30th May 2011, 9:59 pm   #64
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Default Re: 2C34 Project taking off...

Hi, all followers of this thread...

I know about CV18 & VT61/VT61A but I can't seem to locate any datasheets on any of them.
Do you have any, Keith?

I'm almost done with the amplifier; main blocks are fully done.
Still some tidying to be done with NFB-wires; input shielded cables and to decide for stabilized negative supply for the CCS or not.
For the past week the amp's been playing every evening.
It's hooked up to my stereo with a Technics SU-C1000 control-amplifier.
That's the battery-operated model if it means anything to anybody
I've been doing a bit of fiddling to lower the hum-level.
Not that it was ever high but most circuits can be improved.
The 6AN8A was supplied with AC for filaments and the transformer doesn't have a center-tap. That's because the winding was made for supplying Tube-rectifiers fil's. It's a 0-5-6.3V AC winding that is now bridged with 2x100 Ohm in series where the midpoint of the resistors is grounded. THAT cured 50% of hum.
Now, I read somewhere that a RC-circuit across the high-voltage secondary transformer-winding would improve things as well if used with silicon-rectifiers. Mine are super-fast so it won't do much good with cap's across the diodes. I put 22nF/1250V in series with 330 Ohm/2Watt and mounted it across the winding and it again reduced hum.
With fully open input RCA's and the volumepot set to max there isn't ANY hiss to be heard at all and Hum-level is constant at an extremely low level, barely noticeable in front of the speakers.
I can't locate the remainding hum without a scope on hand and that's in the lab. My guess is that the AC filament supply for the 2C34/5687WA's is causing it and I can live with that.
I need to go all the way to the front pentode to introduce hum by touching components and wires. From there on it's dead quiet!

I had a couple of musician friends over the other day. One's a guitarist and the other plays the keyboard. Both vocalists and are just after 50. So, you would think they would pull my poor amp to the ground in a second but they were taken by surprise ...or as it were.
A little Huey Lewis, A little acoustic guitar and some early 60'ies from my CD-player struck them hard
They are still wondering if I'm telling them the truth about the 12Watts

rgds,

/tri-comp

Last edited by tri-comp; 30th May 2011 at 10:05 pm.
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Old 12th Jun 2011, 6:42 pm   #65
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Default Re: 2C34 Project taking off...

Time to wrap things up.
Of course I had to kill a 2C34 when replacing the Anode-leads for something suitably insulated. DO NOT have the Anode-cap's attached and simultaneously work under the chassis with pliers trying to dress the cables properly. These valves are FRAGILE! A firm yank and >>POP<< the Genie is out of the bottle
Oh well, the 2C34/RK34 are very inexpensive ($5 from Vacuum Tubes Inc.) but still it's embarassing.
I'm attaching the final schematics and I'm rather sure they ARE the finals. Measured voltages are added.
I'm very happy with the amplifier as it sounds now, so I don't think there is going to be any changes. At least not until I'll have a chance to finish a LF signal analyzer I'm in the process of building. If it tells me something is wrong I'll of course try to improve things. I just dont think it's possible to improve the design very much given the chosen output valves and transformers.

What I've learned from this first constructing a valve-amp is that the drive-circuit is the most critical stage. My CF/CCS-design is going to be used in the future with other output valves that needs to be driven into g1-current as it performs very, very well. I've plans to test it out on QQE04/5 when time permits. Feel free to use it for non-commercial purposes. Of couse it may be simplified by using a proper transformer for the negative supply. I just didn't have a suitable one on hand and had to use a voltage doubler. Any transformer that will feed the TL783 with around 100V= should keep the chip happy and a bit cooler than in my initial design.

Thanks again to all interested users of this forum that pushed the counter past 3000 in just a couple of months. In a little while I'll start building the next amplifier; an EL34-PP with Lundahl iron. Main chassis is already cut and bended into shape. Sidepanels are being machined right now and then it needs to be painted. A local car painting company heard about my amplifier projects and offered to do a paint job on this chassis just for the fun of it. I wonder where that will take it? Probably I should start advertising for sponsors I'll keep you posted but it's not going to be as interesting as the 2C34 amplifier. Everyone can do an EL34-PP and with Lundahl there's a fair chance it's going to sound very sweet.

rgds,

/tri-comp
Attached Files
File Type: pdf 2C34-PP_5687WA-CF_CCS.pdf (13.6 KB, 341 views)
File Type: pdf 2C34 Power-Supply_IIII.pdf (15.4 KB, 323 views)
File Type: pdf 6AN8A_Pre_Inv.pdf (11.2 KB, 238 views)

Last edited by tri-comp; 12th Jun 2011 at 6:52 pm.
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Old 15th Jun 2011, 7:38 am   #66
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Default Re: 2C34 Project taking off...

Forgot to draw the RC-circuit across the high-voltage secondary winding.
It shouldn't be forgotten as it actually reduces hum quite a bit.

DO NOT experiment with connecting/disconnecting the RC-circuit with the amp. running to see if there's an improvement.
You will draw a fairly big arc when doing so producing very high spikes.
My FRED rectifiers are rated at 600V a piece. 2 in series = 1200V; still not enough to withstand the spike. One string blew and took out the fuse.

Last evening the amp. took a beating as it was playing close to full out for almost a couple of hours. Just to see if anything would crumble. It didn't. X-formers were cold except the power-transformer that was pleasantly warm. Perhaps I overdid the dimensioning of the x-formers
I challenge you to build a better amplifier cheaper. The 2C34 is $5, 5687WA perhaps 2-3 times that and the 6AN8A is probably around $10. Iron from VVT-Transformers goes reasonable and the rest is pretty much up to what you expect to pay for various quality components. A lot of joy for very low pay!

rgds,

/tri-comp
Attached Files
File Type: pdf 2C34 Power-Supply_V.pdf (15.7 KB, 222 views)

Last edited by tri-comp; 15th Jun 2011 at 7:50 am.
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Old 29th Jun 2011, 7:05 pm   #67
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Default Re: 2C34 Project taking off...

The Cathode-Follower/CCS/Push-Pull schematic was re-drawn for a better and more uncluttered view.

Nothing new under the sun.
The amp. still runs every evening to bring a little more joy (read: a LOT more) into my life at the end of the day

rgds,

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Attached Files
File Type: pdf 2C34-PP_5687WA-CF_CCS_.pdf (13.6 KB, 243 views)
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Old 25th Aug 2011, 11:11 pm   #68
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Default Re: 2C34 Project taking off...

Again a small update.
For some very strange reason the 6AN8A's seems to develop a sort of microphony after a while.
They were always sensitive to being tapped gently. Microphonics will be heard which I think isn't unusual.
Then both developed a tendency to 'sing' like oscillating at a high, nearly inaudible frequency. Mind you, it was a mechanical oscillation, not an electrical. Gently re-seating the tube or just holding the envelope caused oscillation to stop.
Now, I have quite a few JAN NOS on hand, so I installed another pair and the oscillation is gone. For the moment at least.
Did anyone experience the same?
Time to consider a replacement and do a re-wiring?
It'll be hard to find a pentode/triode combo that sounds as good, when it's not microphonic of course.
The valve isn't operating anywhere near it's max., btw.
I also tried elevating the filament-AC to +80V to see if it had any influence which it hadn't. Absolutely no difference. Neither in hum-level nor in tendency to oscillate.

Attached the latest, redrawn schematics.
No changes, just re-drawn.

rgds,

/tri-comp
Attached Files
File Type: pdf 2C34-PP_5687WA-CF_CCS_Final.pdf (15.8 KB, 259 views)
File Type: pdf 2C34 Power-Supply_V_Final.pdf (16.7 KB, 191 views)
File Type: pdf 6AN8A_Pre_Inv_Final.pdf (12.4 KB, 185 views)
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Old 28th Aug 2011, 10:55 am   #69
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Default Re: 2C34 Project taking off...

I am curious re 2c34, just had a look on the valve museum and its a transmitting VHF double triode

why use this for an audio amp ? ( but I have no doubt it will work )

I actually was going through my valve collection and I am pretty sure I have got one ( the valve was unmarked so I did not know what it was at the time)

regards

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Old 28th Aug 2011, 10:02 pm   #70
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Default Re: 2C34 Project taking off...

Try fitting some damping rings.....
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Old 29th Aug 2011, 7:47 am   #71
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Default Re: 2C34 Project taking off...

Quote:
Originally Posted by val33vo View Post
I am curious re 2c34, just had a look on the valve museum and its a transmitting VHF double triode
why use this for an audio amp ? ( but I have no doubt it will work ) val33vo
I can give you lots of reasons:

The valve is widely available
It's inexpensive (~ $5)
Hasn't been done before in PP/AB2 to my knowledge (SE:Yes, PP:No, PP-AB2:No)
It's a double, so cheap and easy to do mechanical layout (PP in one bottle)
Full data available on the web including curves
Modest heater requirements (6.3V/0.8A = 5W total for PP, EL84 = 9.5W for PP)
Looks great (imho)
Easy to drive in AB2 (Look at the relatively simple CF/CCS I made)
Sounds Great (..of course I didn't know beforehand)
High output in 'Triode-Mode' 12W/8Ohm, 16W/4Ohm (Of course 'Triode-Mode' )

Sean, Damping Rings may cure the problem, I agree. Just don't want to use valves that require them since it's a fix for bad design/built quality in my opinion.

rgds,

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Old 29th Aug 2011, 7:34 pm   #72
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Default Re: 2C34 Project taking off...

How easy is this design to build for a novice? You say its your first valve amp,but you must have had extensive experience in electronics. As you say the 2C34 is cheap and relatively available,looks good;but how does it compare to a audio pentode or a beam tetrode?

As a novice I find it hard to understand the use of transistors and solid state components in a valve amp outside the PSU. I also notice you have a noval (to me anyway)way of laying out;no use of tagboards. I watch your work with interest,Andy
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Old 29th Aug 2011, 10:00 pm   #73
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Default Re: 2C34 Project taking off...

Andy,

I have extensive experience in electronics. I have been making a living out of repairing the stuff since 1972, but I haven't been constructing anything before, except the odd variable power-supply and small utility circuits.
In constructing and building I'm very much the novice as well but of course, I have the advance of knowing a bit of what to expect when I see a circuit/schematic. With this amplifier the problem was that no schematic was readily available anywhere. So, I read books like Morgan Jones_Building Valve Amplifiers and Morgan Jones_Valve Amplifiers and what relevant material you will find here etc.: http://www.tubebooks.org/technical_books_online.htm

It inspired me to construct and build what you see in this thread. The use of transistors outside the PSU isn't really necessary. The complete CCS-circuit may be replaced with a single resistor as was what was done in the old pre-transistor days. The use of a Constant Current Circuit just enhances the Cathode Follower to make it operate with less distortion and better linearity. Towards an AC-Signal the CCS reacts like an infinite big resistance (Well, pretty much so. At least >5Mohm with these transistors) but still allowing, in this case, a constant DC-current of 3mA to flow through the CF. An ordinary 22K ohm resistor as a replacement to the CCS would allow for the same 3mA to pass through the CF (at quiescent) but now the AC-output of the CF will see a load of 22KOhm and not >5Mohm. Not necessarily a problem with the 5687WA but silicon is cheap so why not grab the opportunity? Also read attachment of posting #18 in this thread.

I have no idea about how the 2C34 triode compares with Pentodes, Tetrodes or other Triodes. I'm about to find out as I'm building an Pentode EL34-PP (here: https://www.vintage-radio.net/forum/...ad.php?t=71791 ). Also a Tetrode-PP is planned (here: https://www.vintage-radio.net/forum/...ad.php?t=70387 ) for the future.
My guess is that output-transformer quality, phase-splitter- and CF-circuits (where necessesary for AB2 drive) will have a bigger impact on sound than the actual choice of valve. ...OK, now I'm in for it!

The layout is done like it is just because I have no easy access to or knowledge of how to make Printed Circuit Boards. Also my way is a heck of a lot cheaper
By using heavy copper-conductors, in my amp as Ground-bus and Negative Supply-bus, they provide fine support for the discrete components of the CCS. The rest is just Point-to-Point terminal-strips (RS-Components 433-775 cut into required sizes) except the Negative Supply which is on a piece of Veroboard.
The real difficult construction to a novice is the chassis. That problem kept me off building amp's for a long time. Now I solved that bit and away we go...

rgds,

/tri-comp

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Old 30th Aug 2011, 7:34 am   #74
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Default Re: 2C34 Project taking off...

Before I'm deemed ignoramous I'll have to correct the meaning of CCS.
What I really should have said is Constant Current Sink
Sorry about that.

rgds,

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Old 30th Aug 2011, 9:34 am   #75
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Default Re: 2C34 Project taking off...

Tri comp
" The real problem was chassis construction " yes there is nothing that spoils a project more than a good working bit of homebrew that has a chassis full of hammer blows where the bends are

i have just bought a bending machine ( I think bending brake is the correct term ) off e-bay for £50 because I am building a paraset replica transceiver

also bought some Q-MAX chassis punches so no more rough valve holes ( They do work a treat but take quite a bit of pressure to punch through the 1mm steel I am using. Got an 8ft x 4ft sheet from the local TATA steel company for £25 so I think it will last me for a long time to come re making chassis

Next project on the design board is a valve tester to my own design

also on the go just now is a speed log for my wee boat designed around a PIC microcontroller, designing the software and de-bugging is the fun part

regards

VAL33VO
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Old 30th Aug 2011, 10:39 am   #76
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Default Re: 2C34 Project taking off...

Since I have access to lasers and bending machines I'm thinking about producing chassis' to customers requirements.
It isn't too difficult adjusting this or that socket and transformer cut-out in Solidworks to cater for specific wishes of the customer. In that way a bare chassis, more or less standardized in main proportions, can be available to anyone wishing to make an amplifier in his/her layout with drop-thru or not transformers. A minimal of punching on the front and rear as for example the mains-filter and Speaker-Terminal holes would already have been cut. Stainless-Steel or ordinary steel on wish. Stainless is a bitch to paint as it needs to be sanded first to achieve good results. Something that wasn't done with my 2C34
Don't really know about economics. Maybe it's not feasible? Is there an interest at all?

Looking very much forward to that valve-tester, val33vo

rgds,

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Old 30th Aug 2011, 11:48 am   #77
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Default Re: 2C34 Project taking off...

Id be interested in a chassis or two. I made my 5-10 out of wood with metal top as theres no way with the tools I have to construct a decent chassis. How much do you think a fairly bog standard one would cost? And to ship? Andy.
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Old 30th Aug 2011, 5:08 pm   #78
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Default Re: 2C34 Project taking off...

I took a few more close-up pictures of the amplifier so you may better see the layout and the construction of the chassis.
Forum-rules are jpg's at 800x600 max. so this is the best I can do.
If you want one of the pictures in higher quality I'll e-mail it to you.


rgds,

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Old 30th Aug 2011, 5:09 pm   #79
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Old 30th Aug 2011, 5:10 pm   #80
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