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Old 5th Sep 2020, 10:05 am   #81
Radio Wrangler
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Default Re: Hope to start an audio amp with CV415/CV4046/TT15

Pulse transmitters?

The usual technique is to have a walloping great capacitor bank big enough that voltage droop along the time of a pulse gives insignificant power droop. Then you need a PSU meaty enough to re-charge it between pulses.

Thr RF stuff has to be meaty enough to do the full volts and amps of the output signal, but with short duration pulses the long-term power>>> heat dissipation is a lot lower than the peak power. The transmitter power device must have thermal mass enough to smooth out the pulses, overall heat sinking can be remarkably small.

A complete transponder (300W out at 1090MHz) with its case, power supply, receiver and TRswitch, logic etc will slide into my shirt pocket. They use a remote control panel.

For this reason, they've become popular with restored vintage aircraft because the tiny panel can fit into their period-correct panel and not look too obvious. They are needed to be allowed to fly in all but a reducing volume of airspace. There are photos of the things on the Trig Avionics website if you fancy a look. Prominent users are virtually all the Red Bull air racers and the RAF battle of Britain memorial flight. Lots of private aircrafr, microlights, gliders. Tens of thousands of aircraft around the world.

David
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Old 5th Sep 2020, 10:06 am   #82
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Default Re: Hope to start an audio amp with CV415/CV4046/TT15

OK David, noted. I will tread with care when I get the boards back, they should make it easier for me to play!

I better get my metal work done so I can hold the board.

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Old 8th Sep 2020, 10:08 pm   #83
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Default Re: Hope to start an audio amp with CV415/CV4046/TT15

The board has finished in production and awaiting the courier, that will take a while to arrive, have made two open chassis/boxes one for each amp, and when I manage to sort out a bigger mains transformer I will do another one for the power supply. Had to actually buy some sheet steel from B&Q! have made them twice the size of the original to help with heat dissipation as each amp will have 14.8 watts of heater and 18 watts of HT to dissipate.

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Did a few measurements of HT current draw today and the total draw was 63 mA, with 52.2mA in the TT15 and g2 zeners. 5mA in the EF91 and 5.7mA in the ECF82. I was happy to see that the total draw did not change from no signal input to output. Of course the wattage should change if I get a bigger B+

I have not bought pcb mounting valve holders as the sockets will be bolted to the metalwork, so will use solid wires as short as possible from the holders to the pc board once I have figured out mounting spacers for the board etc. The TT15 valve holder is deeper than the others.

I need to decide on what I do with the input to the amps with regard to controls, at the moment I just drive directly from the PC, but may consider CD audio or other inputs as well, perhaps I need a small input mixer with tone controls?

It's all fun and it keeps me off the streets.

Thanks for the information David, only recently noticed your post, I must have posted just after you last time and missed it.

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Old 11th Sep 2020, 12:38 pm   #84
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Default Re: Hope to start an audio amp with CV415/CV4046/TT15

Christmas came early, or at least it felt like it, spare CV4046 valve, 5H 200mA choke, HDMI to RCA for my TV playing and the boards from China.

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I did have another invoice to pay, this for DHL sorting out the import duties, so 3.79 paid before delivery.

So next steps will hope to happen over the next few days will be drilling and cutting the chassis, mounting valve sockets and starting to wire up a board, fingers crossed.

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Old 14th Sep 2020, 6:24 am   #85
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Default Re: Hope to start an audio amp with CV415/CV4046/TT15

Nifty boards, nice work, look forward to seeing the finished amps. I find with amps it's a good idea to be flexible in case you want to make changes later on. Tone controls are nice to have especially if you don't use them, bit like an ejector seat in the jalopy. Same with ins and outs, you never know what your going to get up to in the future, easier to drill the holes now than later, you can always cover em up with a plate.

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Old 14th Sep 2020, 11:10 pm   #86
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Default Re: Hope to start an audio amp with CV415/CV4046/TT15

You build something, it looks scruffy with the component layout, a few instability problems sorted by a 100 pF cap (anode hf bypass) but at the end it all works and sounds OK.

So you do a board layout, get feedback and change a few things. Get the boards made, go bigger with the metalwork to act as a bigger heat-sink, spread the valves further away from the transformer so it does not get direct heat etc.

You wire components up, add the output transformer, get the valve bases connected and do a temp connection from the power supply and to the speaker, have bits of audio cable from the PC to the input. You then power it up and listen to a song or two!

So, why the hell should I be so surprised when it appears to work? It's to late to start with the scope and multimeter to check every voltage tonight to see if it meets previous specs, but wondering why I have to think it would be a failure?

I can only guess apprehension after the time and effort.

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Sorry for the temp connections, with the heater wires I will be trying some hot glue to anchor them to the board.

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The chassis is approx 244 x 150 x 40mm I need to contemplate a heat-sink from the aluminium valve collar to the chassis, the valve holder on this one is proud of the chassis so the TT15 base does not sit on the chassis to dissipate any heat and the aluminium collar soon gets very hot. I remember a metal clip on the aircraft set between chassis and valve base, but I assumed it would be to keep the valve in place, the aircraft radio also had forced air cooling!


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Old 16th Sep 2020, 7:26 am   #87
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Default Re: Hope to start an audio amp with CV415/CV4046/TT15

Nice work Adrian. My projects often don't work first time mainly because in my haste I often forget to connect something or plug the DUT in.

Heat issue's often arise with amp builds because it's often neglected and hard to design for at prototype stage unless you have some whizz bang measuring gear and software. Your a bit limited there as you can't drill holes to allow for a bit of up/through draught/convection because of the PCB. Still, shouldn't be a problem if you don't have kids/pets, just put a "HOT" sign on it.

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Old 16th Sep 2020, 8:17 am   #88
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Default Re: Hope to start an audio amp with CV415/CV4046/TT15

Hi Andy.

In theory I could put holes in the chassis, there is around15mm space between the board and metal. I have been thinking and have a possible solution, somewhere I have some silicon-heat transfer mat and I am pondering placing it under the valve around the socket. Or I make a finned heat-sink to slide on the aluminium skirt, it is already connected to ground so the fins would have no effect at audio!

I need to find my IR thermometer to actually see if it is an issue or not, but you certainly would hurt your fingers.

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Old 16th Sep 2020, 2:53 pm   #89
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Default Re: Hope to start an audio amp with CV415/CV4046/TT15

Graph in #1 will no doubt remind some folks of C & G Radio & Line A.
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Old 16th Sep 2020, 10:54 pm   #90
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Default Re: Hope to start an audio amp with CV415/CV4046/TT15

Started to build up the second amp today.
I bought a mains transformer after briefly looking at specs, and I may have gone a bit over the top!

To mount that transformer I need some thicker steel, it weighs a bit, have a GZ34, 5H 200mA choke and a 50 +50 uF cap at 500 Volts to build the power supply. Need to get fuse holders mains socket and a big switch.

I think my challenges will be to decide on how to inter-connect it all plugs and sockets wise, pick the final layout, and to pick it up when finished.

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I could go for some tone controls and a pre amp build later, buy one of the Chinese, valved pre-amps from Ebay, but feel I would need to replace the plug top PSU. But I would still have to decide what sources to use with the amp. i.e. CD player, Record deck etc. Or.

Seeing if I can use a HP Thin client, as a Media Player, something that can hold the music and send it out via headphone/line out to the amps direct, and control it via a web page.

Up to now I have tried Volumio with success, Linux mpd and failed and looked at Linux gnump3d, but that seems to have stopped development in 2007.

I am not after a Media Server as I do not wish to have it streaming mp3's across the home network to other devices. All just ideas for now.

Perhaps some more knowledgable people here could suggest a simple media player that is simple to install (Linux Ubuntu 16.04).

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Old 17th Sep 2020, 9:30 am   #91
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Default Re: Hope to start an audio amp with CV415/CV4046/TT15

Hi Adrian

I think I may have an Apple ipod hidden away somewhere - you could use it as an audio source and drive your amp from the headphone output.

You'd need itunes to load it up and it may already have several gB's of music on it !

Let me know and I'll have a dig around for it.

73 Tim
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Old 17th Sep 2020, 2:02 pm   #92
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Default Re: Hope to start an audio amp with CV415/CV4046/TT15

Hi Tim the app Volumio works fine on the thin client, can control it via a web page from any mobile device etc. I was just wondering about other packages that are available, as always at this end seeing what I can do with what I have to hand.

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Old 18th Sep 2020, 6:22 am   #93
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Default Re: Hope to start an audio amp with CV415/CV4046/TT15

That's a gurt big beast of mains tfmr, you could always use bracing under it. I have some fuse holders you can have and mains rated rocker SW's, drop us you address and they're yours for the postage.

Re preamp I used te Rod Ellliot preamp in my last amp, he does PCB's, it's SS though.

Andy.
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Old 18th Sep 2020, 9:33 am   #94
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Default Re: Hope to start an audio amp with CV415/CV4046/TT15

Thanks Andy for the offer, I may get back to you, I need to go through my boxes for bits first to see what I have. I tend to use filtered IEC sockets for the mains where I can.

I should be getting steel in the next few days with luck so I could then sit down and plan the PSU section.

Today is a nice day, my kit car passed it's MOT yesterday, so today will be out on the road.

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Old 23rd Sep 2020, 6:41 pm   #95
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Default Re: Hope to start an audio amp with CV415/CV4046/TT15

Quote:
Originally Posted by bikerhifinut View Post
Just a note on EF86, they are horribly expensive, even the Russian ones.

A.
I've found the 6BR7 is fully as good as the EF86, and generally much less pricey. Like the EF86, it was designed as a low-noise, low hum, low microphony preamp.

EF91s are great at RF but horrible as audio preamps - invariably noisy and microphonic.
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Old 23rd Sep 2020, 7:24 pm   #96
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Default Re: Hope to start an audio amp with CV415/CV4046/TT15

I have read several comments on the EF91 like that in this thread and to be honest the only time I had the issue was down to the amp self oscillating at 1.25MHz, once that was cured they are fine, I am not finding them microphonic, I can tap them and they do not ring in the speakers when I last did a measurement of peak signal to noise I obtained a reading of 74.6dB. The measured distortion on my last test with the amp was 0.2% at something like 5 Watts output.

Is it Hi-Fi, no I guess not, but this project has already achieved something for me, building something with odd-ball valves that seems to work. I put it down to the Millar/Radford design and good transformers. By the way the EF91's in use are in fact CV4014/M8083's which are a military version and from the National Valve Museum's page is this comment:-

"The M8083 is a special quality version of the EF91. The M8083 has a more rugged build than the EF91 and was designed for applications where vibration during operation was unavoidable and where the performance could be predicted when subjected to such vibration. The obvious application is mobile communications especially military."

Still awaiting some steel to make my final PSU chassis which should give me the required HT to have over 10 Watts audio, I hope?

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Old 24th Oct 2020, 10:31 pm   #97
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Default Re: Hope to start an audio amp with CV415/CV4046/TT15

This little project was a bit delayed with the Ferguson TV and awaiting some steel sheet. The chassis for the PSU was done the same as for the amps but in 1.5mm thick steel to take the weight of the transformer.
Add a GZ34 a couple of HV caps and some wires. Then decided I need to move it all somewhere and keep it as one unit, so out with the Plywood and wood stain to build a small cabinet to house it all. PSU underneath as that is the heaviest.
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Still being driven by a PC running Volumio and quite enjoying listing to music. A bit of Billy Idol and White Wedding at the moment.

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Old Yesterday, 11:01 am   #98
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Default Re: Hope to start an audio amp with CV415/CV4046/TT15

Hi Adrian you do right to have it on display after all the effort that has gone into it ,I looks wonderful, well done , I have just got the EL508 amp tamed , it's now no longer a transmitter . You must play Time, by Pink Floyd at some volume the clocks were recorded in various antique shops, Mick.
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Old Yesterday, 11:47 am   #99
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Default Re: Hope to start an audio amp with CV415/CV4046/TT15

Hello Mick,

I do have that album, Dark side of the moon.
I bought a couple of very cheap passive tone boards from China with the possibility of adding them to the amp later, for the price I could not even buy the parts.

OK on your EL508 amp, you will have to update your thread on it, I like pictures.

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