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Old 6th January 2009, 12:27 AM   #1
BusShed is offline BusShed  United Kingdom
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Default sorry, yet another newbie - what can I make with these???

Hello all, sorry for will probably turn out to be another newbie question, but hopefully from a slightly different angle...

Firstly, I know very little about tubes. I know they use lots of voltage, and glow nicely... I am pretty happy playing with electronics, and have some background in pro-audio although not in a design capacity.

So, some years ago I was given a small pile of valves, which I then stashed away in a cupboard at my parents place. Over Christmas said pile has come back to light and started me thinking what I could do with them. They are all mullard tubes with the following markings:

ECC83
EZ80
EF86 (x3 off)
EL84 (x2 off)

These numbers seem to correlate to a number of mullard designs (3-3, 5-10, 5-20) that I have dug up on the internet, but none of which do quite what I want to do as a first valve project. So, I have a few questions...

Since the best thing o start of with is something you actually want, I would like to build a small amp for my ipod (don't laugh). I have a couple of pairs of speakers available for use (one pair are 6 ohm and one are 8 ohm impedence).

So question 1:

All the designs I have found which use these tubes all also talk about a preamp being required. I am assuming that by using my ipod at line level as a source I don't need to worry about preamps... does that hold true?

question 2:

Are there any better designs for amps which utilise the tubes I have which give me a stereo amp or reasonable output? I am not averse to aquiring some more if required, but would really like to make use of these tubes.

question 3:

Can anyone suggest any good sources of transformers and bases for these tubes in the UK?

question 4:

How much does the impedence of the speakers matter to the overall performace of the amp? In the big stuff that I use, everything is at least 8 and some is 16 ohm impedence...

As I said, probably some really dumb newbie questions, but please be gentle...

Cheers
Mark
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Old 6th January 2009, 01:32 AM   #2
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I suggest selling the tubes and using the money to finance part or all of a new amp.
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Old 6th January 2009, 01:46 AM   #3
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Mark,

Just so you know, if those tubes are NOS (new old stock), you are looking at money. Mullard made tubes are QUITE desireable.

You could build a "5" WPC, single ended, pentode mode, stereo amp from the ECC83/12AX7 twin triode, the 2X EL84 power pentodes, and the EZ80/6V4 rectifier.

Selling the EF86s off could provide a nice "chunk of change" to help cover your expenses.

Sowter plus Stevens and Billington are UK sources of tube amp magnetics.
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Old 6th January 2009, 03:06 AM   #4
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Quote:
Originally posted by Eli Duttman
You could build a "5" WPC, single ended, pentode mode, stereo amp from the ECC83/12AX7 twin triode, the 2X EL84 power pentodes, and the EZ80/6V4 rectifier.
Our RH84 derived monobloks use EF86 strapped in triode driving EL84. We used EZ81 in a hybrid bridge.

dave
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Old 6th January 2009, 05:56 AM   #5
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You mentioned the Mullard 3-3 among the designs that don't do what you want to do. Why is that? You could buld it without the tone control.

I agree, you shouldn't need to use an active preamp if the input signal is at line level. A volume control should do the job.

Regarding the speaker impedance, the only difference it makes is what ratio output transformer you need to use to match it to the OP tube loading requirement.
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Old 6th January 2009, 01:47 PM   #6
BusShed is offline BusShed  United Kingdom
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Thanks for the replies chaps, much appreciated.

The mullard valves are all boxed, and I believe them to be new (except the ecc83, which is in the wrong box), but I hadn't realised they were particularly valuable - does anyone have any links or ideas of what they might be worth? I am curious

ray_moth - the 3-3 I had not entirely discounted, other that in the versions I had found it is only a single mono amp as I haven't found a stereo version of it yet. Also the 3W output is a little low. Stereo versions of the 10 or 20W version seemed more appropriate. Thanks for the confirmation on the other points.

planet10 and Eli - your suggestions sound good, although I may have to do some reading to fully translate! Does anyone have any links for schematics or circuit designs for these systems or would it be a case of having to design something myself?

As I said, I am really a novice at the design side of this...

Thanks for your help, any more suggestions gratefully recieved.
Thanks
Mark
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Old 6th January 2009, 05:10 PM   #7
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Mark,

You can't get more than 5 WPC from 2X EL84s. The Laws of Physics are totally unyielding.

Extracting the value from the NOS would give you a financial head start on a project whose O/P power is more to your liking.

A very, very, very, nice 12 WPC ultralinear (UL) mode "El Cheapo" could be built employing Sowter's model U082, for the O/P trafos. The LENGTHY saga of "El Cheapo" is here.

BTW, a stereo amp is simply 2 mono channels. The power supply has to be competent and, as a consequence, that portion of "classic" designs must change. However, the signal topology is, with a few minor modernizing modifications, merely replicated twice.
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Old 6th January 2009, 05:38 PM   #8
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Quote:
Originally posted by Eli Duttman
You can't get more than 5 WPC from 2X EL84s. The Laws of Physics are totally unyielding.
Our amp clips at 3.8 w.

Quote:
Extracting the value from the NOS would give you a financial head start on a project whose O/P power is more to your liking.
There is a lot to be said for that. The value of NOS Mullards is quite staggering. The EL84s in particular are nice valves, but within a budget, spendin money on things like Solens for the power suppy will yeild more gain.

dave
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Old 6th January 2009, 05:41 PM   #9
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Quote:
Originally posted by BusShed
The mullard valves are all boxed, and I believe them to be new (except the ecc83, which is in the wrong box), but I hadn't realised they were particularly valuable - does anyone have any links or ideas of what they might be worth? I am curious
Search "Completed Listings" (Small box on the left) in eBay for Mullard EL84 or Mullard EF86 to see what kinds of prices people have been paying. You might need to register with eBay to do this. Then come to your own decision about what price to ask either here on the forums or eBay.

Also: What efficiency are your speakers? That should be the first and most fundamental question when deciding what kind of tube amp to build.
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Old 6th January 2009, 06:07 PM   #10
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Default fwiw...

build with what you have. Forget about what you want in terms of output power - its going to be irrelevant once you get hooked on tubes anyway. The research and practice involved in simply building anything with those tubes will be the most valuable part of the whole experience. Best bit is - if you don't like what you hear at the end, the tubes are still resellable - they are not irrevocably committed to the circuit. Don't forget to keep the boxes pristine!!!

There are heaps of real simple EL84 based SE circuits around that will match your tube line-up, a couple of which have already been mentioned here. Choose one you like, and build it.
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