1St Tube Amp

[dhaen]

Actually I do like it, along with other delicacies like Icelandic dried fish......delicious....

There is an ostrich farm about 3Km from my house.
The steaks are tough......but biltong's an idea My workshop gets hot enough in summer

Cheers,

[EC8010]

Bas has suggested a single-ended amplifier on the grounds that the circuit is simple, and this is true. Unfortunately, single-ended amplifiers are less forgiving of imperfect construction than push-pull. There isn't a free lunch...

Sadly, there isn't a definite answer to your question. I just know I'll be flamed for this, but if you prefer Led Zeppelin to Miles Davis, then go push-pull ultra-linear EL84 or EL34, otherwise, you're looking at 2A3 or 300B single-ended. (Gross simplification.)

(I have single-ended, push-pull, silicon, and germanium.)

[fdegrove]

Hi,

Try OTL. It will pervey all kinds of music truthfully.

[fragman56]

Single-ended triodes are simple to understand and construct. But, how do you feel about low wattage (1.95 for 6bq5, 2.5 for EL 34, etc.)?

Push-pull will get you plenty of power for home listening.

Joel has a couple of nice ones in this forum--I built his 6bq5 and I think it sounds great.

There is another really interesting one buried in this forum that is a DC-coupled 6em7 with battery bias. It is SET.

Good luck, sounds like you have plenty of electronics experience.

Rick

[JDeV]

Since I do not want to spent alot of money on something I might get smoking, I decided to build an amp with components I already got, which includes a 220-0-220, 0-6 , transformer from old tube radio, EL84, 12AX7A anb EZ81.

Questions I have so far:
1) This circiut, from somewhere on the net, use a 265-0-265 transformer, will mine be O.K. ?
2) I only got 100uf, 220uf, 330uf and 470uf caps - 8 of each, in 400V. Can I use any of them on PSU instead of 47uf?
3) What wattage must PSU resistors be?
4) The inductor in PSU is 10H, to wind 1 myself, how many turns of what gage wire around what? (Air core, ferrite??)
5) I got an OT , also from old radio, not sure of its specs. Can it be a problem just to try it anyway, circuit do not show any specific value for it. I plan to use 88dB, 8 ohm speaker on amp.

Circuit:

[EC8010]

(1). You will lose power by only having a 220V transformer rather than 265V
(2). Valve rectifiers are far more fragile than their silicon brethren. 50uF is the maximum permitted reservoir capacitor for EZ80 and EZ81 to avoid excess ripple current. (Of course, you could always put a pair of 100uF in series with 220k across each to balance leakage currents.)
(3). Well-ventilated 3W should be fine.
(4). Forget winding your own chokes. 10H is a large inductor. They can be bought. They have iron cores.
(5). According to Mullard, EL84 needs to see 5k load. From an 8R load, that means you need a voltage ratio of 25:1. Check your proposed transformer to see if it is that ratio.

[bournville]

Jdev,

If you are cannibalising parts from your Pilot radio, mentioned in another thread, to make this amp then the output transformer you intend to use, currently connected to an ECL86, will give an output to 3ohm rather than 8ohm. An ECL86 has a slightly higher anode load than an EL84, but the amp should work despite this slight mismatch, but remember than the EL84 has a higher anode current than the ECL86 (especially if you use a higher power mains transformer). An output tranny designed for an ECL86 might not be able to handle the higher current requirements.

[JDeV]

Originally posted by EC8010
(1). You will lose power by only having a 220V transformer rather than 265V
(2). Valve rectifiers are far more fragile than their silicon brethren. 50uF is the maximum permitted reservoir capacitor for EZ80 and EZ81 to avoid excess ripple current. (Of course, you could always put a pair of 100uF in series with 220k across each to balance leakage currents.)

What will happen if I use a normal silicon bridge in place of EZ81?
If I had used the 265V transformer, I would have lost about 50V trough the EZ81, is that correct? Then ended up with about 215V.
If I use a silicone bridge I will only loose about 1.5V, ending up with 218V. Will this be a good idea or rather not?
If idea is O.K, can I then use the 100uf caps?

[EC8010]

Originally posted by JDeV
What will happen if I use a normal silicon bridge in place of EZ81?
If I had used the 265V transformer, I would have lost about 50V trough the EZ81, is that correct? Then ended up with about 215V.
If I use a silicone bridge I will only loose about 1.5V, ending up with 218V. Will this be a good idea or rather not?
If idea is O.K, can I then use the 100uf caps?

It's a liitle bit more complex than that. AC mains is specified in RMS volts. For a sine wave, the peak voltage is 1.414 times higher, so your 218V transformer produces 308V peaks. If you use a silicon bridge and 100uF, the capacitors will charge to nearly the peak voltage of 308V, whcih will do you nicely for the EL84.

If you go the the Duncanamps site, there is quite a nice little piece of freeware called Power Supply Unit Designer (PSUD). Have a play.