Let's fix a Blackstar HT20 1 X 12 Combo
Вставка
- Опубліковано 20 вер 2024
- Blackstar HT20 1 x 12 Combo This amp came in with output tube problems. The amp is fitted with EL84 Ruby Tubes. Is it the tubes or the amplifier circuit that's at fault. We delve and take a look.
Cracking vids, I've been tying to sort a WEM dominator mkIII, It came with a cracked valve (one of the 12ax7's), and a split resistor over the main filter cap, I've got it running, thanks to your tip about the first and 2nd pins not being interconnected on the newer EL84's and having to unsolder the white wire from pin 1, to pin 2, thanks for that :-), it runs nice and clean on the 2nd channel but only noise from the first, and when I turn the bass or treble up it kinda works for maybe 1/4 to 1/2 a turn then the volume seems to get lower and disappear, Its the same on both channels, I've tried changing the pots and ended up putting the original cts ones back in, I changed out the electrolitics in and changed the green square caps, also changed one of the mustard caps as dc seemed to be leaking to one side. Been checking various resistors, I'm still messing about with it, I'm waiting an a set of resistors coming, I was just going to change them all, seems like overkill, but its driving me potty. finding it had to relate from the schematic to the components on the board, but I'm slowly getting there., been watching your vids, some cracking info, has helped me no end. yer playing is a joy to listen to as well 🙂. Any advice you could offer would be appreciated, if you have time, All the best big yin :-)
Hello. Go to my channel home page. Click where it says more links. Scroll down to where it says view email address. Drop me an email with your contact details. Take care.
Nice job and enjoyed the playing at the end. Appreciate all you do to produce these videos and I always learn something mate. Thank you sir!!
Hello JT, thank you. Thanks for watching and supporting the channel. Take care.
Just shows that simply following the recommended 7 watt bias on EL-84's is not always the right thing on some amp designs. Nice sounding amp and some great playing.. Many thanks Martyn.
Hello Pete. I think I am going to use the scope more for biasing some amps. Certainly on these modern amps it make s sense. Take care Pete.
Nice to see someone else setting bias with a scope!
I prefer to use Analogue instruments.
At today's prices I don't like new valves to have any unnecessary stress.
I have a Leader Stereo Millivoltmeter permanently connected with a BNC tee junction to my scope probes, i can read RMS voltage straight from the output/ dummy load with the scope probe. One connection does the test, I don't even need to ground the scope probe.
Hello Alan. I think with these modern amps it's the way to go. The power transformers seem so underrated. And as you say modern tubes are not great, especially the JJs. That sounds like a good set up you have going there. Thanks Alan and take care.
It’s not just the valves that cop a hammering at high bias but with a pcb like that the extra heat would certainly shorten its life
Hello Mark. Yes, The heat take it toll over time. The power transformers on these newer amps are not great either. they can get extremely hot when these amps are cranked. Take care Mark.
Thanks again for a great video. Did you use the signal generator on the Hantek scope? if so is it any good, I was thinking of getting one for my bench....
Hello Jools, thank you. Yes I did. It works fine and saves desk space. This scope is okay for what I use it for. Take care Jools.
02:57 left tube is microphonic, so after you replace the right tube, the problem persists... 4:00
The right tube was arcing inside. The left tube was indeed micro phonic. Those tubes had been worked hard. Take care.
" Who wants yesterday's Ruby Tubes-day/ goodbye to yesterday's girl......" 😉
Ye, they were not great tubes by the look of them.
Hi Martyn, was that the output transformer you was doing the bias with only I thought they were ac volts not dc like you had on your meter..
Hello Keith. It's the secondary of the output transformer that is AC. I was testing on the primary, which is DC. Thanks for watching and take care.
Those Ruby's may be JJs. Or Sovteks or China. Ruby does not make tubes.
Hello, thank you. I keep seeing them now and again, in mostly in cheaper amps. I have never seen a set in a Blackstar before. I never really looked in to them. Just assumed they were all Chinese tubes. I will have read up. Thanks for watching and take care.