FSHZ:42 said:
The whole point is to remove any gas in the envelope so it won't help new tubes. The high temperature re-activates the getter. I used to believe that it also would help rejuvinate the heaters, but this is apparently less likely...
I hate to admit it, but most old tubes DO sound better than current production. If your amp has cheap looking east german EL34's then I would DEFINITELY cook them. They are EXCELLENT tubes...
Then you can decide to do something else that will make a really BIG difference like change the cathode bypass caps to something decent...
Also:
If you have never gone into an amp then PLEASE read the sticky thread at the top of the forum regarding safety practices.
The HV caps hold a LOT of potentially LEATHAL voltage. They need to be emptied of their charge before you start messing around with a soldering iron... PLEASE read that thread.
Tip #5:
If it has a volume control then replace it with a stepped potentiometer. A stepped pot will definitely sound better than a cheap carbon pot (especially once it's run-in). You can often find nice quality ones already built on fleabay for 25 dollars from hong kong or taiwan. Again, make sure it will fit first.
Tip #6:
Change the Electrolytic Caps in the power supply. 'Lytic caps don't last forever... Use low ESR 105 degree caps. Do the smaller Electrolytics first and see how it sounds.
Ok. 'nuf said.
soulmerchant
Thanks once again for this these tips. If you look at Post #4 you can see a picture of the amp that I have. There are 4 power tubes model# 6CA7/EL34A, most likely Chinese, and 4 pre-amp tubes model# 6N3, these also are most likely Chinese. I will try and post a picture of the inside soon, and maybe you can advise me what I should do.
P.S. Do you have the link for the thread regarding the safety practices?
Thanks,
FSHZ:43
Thanks once again for this these tips. If you look at Post #4 you can see a picture of the amp that I have. There are 4 power tubes model# 6CA7/EL34A, most likely Chinese, and 4 pre-amp tubes model# 6N3, these also are most likely Chinese. I will try and post a picture of the inside soon, and maybe you can advise me what I should do.
P.S. Do you have the link for the thread regarding the safety practices?
Thanks,
FSHZ:43
soulmerchant said:
Hi soulmerchant,
Being a bit of valve/tube newbie, I'm curious to know why changing the cathode bypass caps has an effect on sound...? Can you explain?
I'm having a play with an amp I've bought on ebay, and this sounds like another thing to try.
I'll agree with the other comments in the thread regarding replacing other caps in an old amp. A few years ago I rebuilt a Heathkit S99 (I think) amp - replacing the dodgy old caps increased the volume significantly, and brought the sound "back to life". Seem to remember it was changing the interstage coupling caps that made the difference....
Cheers,
ChrisC.
hnb2907 said:
You have audio signal on the cathode... unbypassed it provides local negative feedback to the tube lowering the gain of that stage. When (if) the design calls for cathode bypass caps - you are essentially using the capacitor to short circuit this audio signal to ground so that it does NOT provide any feedback/gain reduction. So, a cap that does a bad job at this will actually leave a residual AC signal that doesn't really resemble the audio waveform and is detrimental to sound itself. Follow?
Yep, got it! Thanks for the explanation.
That now explains something that I see in the schematic diagram of the amp I've just bought (check thread "New Toy")....
The EL34 has a cathode bypass cap, whereas the input 6SJ7 connected in a similar configuration has the speaker output connected at the cathode, to provide negative feedback.
My electronics background is mainly in digital, and I'm a bit of a valve (analog) newbie, hence the daft questions!
Cheers,
Chris.
That now explains something that I see in the schematic diagram of the amp I've just bought (check thread "New Toy")....
The EL34 has a cathode bypass cap, whereas the input 6SJ7 connected in a similar configuration has the speaker output connected at the cathode, to provide negative feedback.
My electronics background is mainly in digital, and I'm a bit of a valve (analog) newbie, hence the daft questions!
Cheers,
Chris.
hnb2907 said:
Please note that is a GLOBAL feedback loop - not just local - and it is in addition to the local feedback of that single stage. Remember current flows through the cathode, tube and plate resistances and the cathode and plate circuits are out of phase with each other. A common phase splitter uses this fact and places even loads in the cathode and plate and thus you have out of phase signals at each. The concertina splitter (as it's called) is not used much though because they output impedances of each circuit are not the same and also because of the equal loads - there is no gain in that stage.
Think of one single triode stage... while keeping the plate resistance fixed, raising the value of the cathode resistor will lower gain because you will generate a larger and larger out of phase AC signal over that resistance...
I have one of these VAL VP-110S. I bought it during the late 90's when Parts Express had them for sale.
I've tried WE 396A/2C51, Raytheon 2c51, JAN 5670, russian 6n3p, and the original chinese 6n3 (military grade J).
The most luscious sound came from the badly overpriced WE 396A. The sound was likely too lush. The most analytical came from the JAN 5670 and the midrange suffered badly.
I hate to say this, but the original Chinese military grade 6n3 actually have good balance and works the best for me. And the tubes are about a cm taller! The Russian 6n3p will give you more detail than the original but without the harshness of the 5670's.
The original EL34's should be replaced with something else. I have svetlanas in there now. I think I should try the new KT77's at some point.
I've done various things to mine including trying various capacitors. 0.47uF Orange drops replacing the original unknown metal film types improved things. I tried various exotic caps with barely any difference. I was planning on trying some paper-in-oil types eventually.
One thing I tried once was replacing the OPTs with Dynaco A470's (potted variety) and the sound was more extended. I think the original VAL OPTs could be better but they are actually a symmetric design unlike the Dynacos. I measured the OPTs to be 5k p-p.
The power transformer is especially beefy and has taps for 230V primaries. The odd thing is that they have an "audiophile" type cap specifically located as a bypass for the output of the solid state rectifier. I've never heard of the brand, but it's really fancy with gold lettering.
The driver tubes sit on a FR4 PCB which is well laid out. The board design was actually done well. Assembly is top notch.
These are actually decent amps and taken as a whole perform better than my heavily modified ST-70.
I've tried WE 396A/2C51, Raytheon 2c51, JAN 5670, russian 6n3p, and the original chinese 6n3 (military grade J).
The most luscious sound came from the badly overpriced WE 396A. The sound was likely too lush. The most analytical came from the JAN 5670 and the midrange suffered badly.
I hate to say this, but the original Chinese military grade 6n3 actually have good balance and works the best for me. And the tubes are about a cm taller! The Russian 6n3p will give you more detail than the original but without the harshness of the 5670's.
The original EL34's should be replaced with something else. I have svetlanas in there now. I think I should try the new KT77's at some point.
I've done various things to mine including trying various capacitors. 0.47uF Orange drops replacing the original unknown metal film types improved things. I tried various exotic caps with barely any difference. I was planning on trying some paper-in-oil types eventually.
One thing I tried once was replacing the OPTs with Dynaco A470's (potted variety) and the sound was more extended. I think the original VAL OPTs could be better but they are actually a symmetric design unlike the Dynacos. I measured the OPTs to be 5k p-p.
The power transformer is especially beefy and has taps for 230V primaries. The odd thing is that they have an "audiophile" type cap specifically located as a bypass for the output of the solid state rectifier. I've never heard of the brand, but it's really fancy with gold lettering.
The driver tubes sit on a FR4 PCB which is well laid out. The board design was actually done well. Assembly is top notch.
These are actually decent amps and taken as a whole perform better than my heavily modified ST-70.
Cycline3 said:
I would say in this case old isn't better than new. The problem with those low-cost kit type amplifiers from the past is that they were never meant to be the best of their time. The ST-70 could be characterizied as barely hi-fi even then.
The ST-70 for example have those output transformers with their patented winding technique. They were designed that way to be easier to construct, not really for any superior technical reasons. One only has to compare them to something from the same vintage like the peerless 20-20 types with transformer cores with nickel and sophisticated interleaving.
The stock driver circuit is basically a low-cost approach. By using the 7199, they reduced the parts count. It certainly does the job, but it could have been done better.
I have many different amplifiers from the 50's and 60's and I would say the VP-110s is better overall than the Dyna ST-70, but I wouldn't say it's better than something like my Allen organ amps or my Heath W-5m's (even with their flaws).
There were very good kit amplifiers back then, I just wouldn't say the ST-70 was one of them even with its popularity. Then again that ST-70 would kill just about any solid state amplifier build until the early to mid 80's.
The VP-110s isn't the last word in EL-34 amplifiers, but it's at least a good attempt to make an amp without a whole bunch of compromises. And they did a smart thing by choosing a high performance driver tube that is common and cheap and comes in many different makes from all over the world.
walker112 said:
6n3p is in principle a very nice tube - nice linearity, low distortion and gain of 33 - but I there is way too much production variation.
I must be honest though - I don't like orange drops very much. If space+price is an issue I would go for ERO MKT 1813 if you can find them.
The Mundorf M-cap to be a good current production alternative, but for the same price you could get a russian K40Y-9 PIO.
This is probably a nice sounding PP, but it would be silly to spend a lot on fancy botique caps. 400V rated 0.47 jenson or jupitor currently cost about $20 each...
Similar rated K40Y-9 on fleabay (still) go for about $3 each. not a tough decision there. There are even cheaper russian PIO (K42-Y2), but I haven't bothered to try them.
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