Search found 57 matches

by Wolfgang
Tue Jan 15, 2019 3:09 pm
Forum: Everyones Projects
Topic: Remember These?
Replies: 504
Views: 15891

Re: Remember These?

I am really tempted in the meantime to try something with this 13E1 (NOS from the 1960 or later ?) myself. Just starting with one tube for experimenting. The biggest limitation with the 6C33 was the 60W max which was easily reached with 470mA/130V and the necessary min peak output power even for 15R...
by Wolfgang
Sun Jan 13, 2019 3:01 pm
Forum: Everyones Projects
Topic: Remember These?
Replies: 504
Views: 15891

Re: Remember These?

The best part of using the 6H30 is that it ca be easily replaced by a 6H6p or 6H1p and more. My guess is, from listening to all 3 tubes in my sound systems (AR, SE OTL ), that a 6H30 might sound too sterile in a single output tube OTL. The 6H6p might sound warmer with more bass, the 6H1p a little mo...
by Wolfgang
Sun Dec 30, 2018 3:16 pm
Forum: Everyones Projects
Topic: Remember These?
Replies: 504
Views: 15891

Re: Remember These?

It’s really about protecting the output tubes in OTLs from extreme stress every time the amp is turned on. It also depends on the amp type. In case of PP OTLs a soft start is recommended to protect some of the tubes from conducting initially a lot more current than for what they have been set up in ...
by Wolfgang
Sat Dec 29, 2018 8:19 pm
Forum: Everyones Projects
Topic: Remember These?
Replies: 504
Views: 15891

Re: Remember These?

I noticed that the resistor for setting the current with the TL783 is not at the output where it should be. Just a typo? The 0.1uFcap between the 2 triodes of the input stage was part of the phase problem with the feedback loop in the original 300B OTL DC which caused the motorboating/bass driver pr...
by Wolfgang
Sat Dec 29, 2018 1:23 am
Forum: Everyones Projects
Topic: Remember These?
Replies: 504
Views: 15891

Re: Remember These?

To cut a long story short, the feedback resistor is now 3K3 as opposed to the 4K2 it had been. The result of the increased feedback is excellent and has both evened out, and tightened the bass up very nicely. I decided to use ears rather than scope and sig gen to fine tune the feedback to my own ta...
by Wolfgang
Thu Dec 27, 2018 3:43 pm
Forum: Everyones Projects
Topic: Remember These?
Replies: 504
Views: 15891

Re: Remember These?

What are your concerns with the voltage doubler and what will you use instead in this position? What kind of psu do you use now for the 13E1? This might be also interesting for using the 13E1: I finally added a socket/made the necessary connections for testing the 6C33 with my TS tube analyzer. It's...
by Wolfgang
Thu Dec 13, 2018 6:43 pm
Forum: Everyones Projects
Topic: Remember These?
Replies: 504
Views: 15891

Re: Remember These?

I cannot see at the moment how we could integrate the hall sensor for monitoring the current. But maybe there is a way? The digital output could trigger a SSR. I use CMOS Hex inverters for this in my circuit.... so it would go in the same direction. A very simple but not very precise/practical solut...
by Wolfgang
Thu Dec 13, 2018 3:58 pm
Forum: Everyones Projects
Topic: Remember These?
Replies: 504
Views: 15891

Re: Remember These?

That’s why Steve’s experience with the blown cap/arcing tube was a wake- up call for me. Add to it that these kind of amps really respond very accurately to whatever is done to them no matter where -and you don’t want to ruin the SQ! - and you find yourself very quickly stuck between a rock and a ha...
by Wolfgang
Thu Dec 13, 2018 3:59 am
Forum: Everyones Projects
Topic: Remember These?
Replies: 504
Views: 15891

Re: Remember These?

Nick wrote: ↑ Wed Dec 12, 2018 2:48 pm Mike H wrote: ↑ Wed Dec 12, 2018 7:40 am One thought that occurs to me is you could use something that is based on a high Voltage MOSFET. Which won't care if its drain is taken up to HT level. You could use a mosfet as a cascode above the CCS, but it will eat ...
by Wolfgang
Tue Dec 11, 2018 8:43 pm
Forum: Everyones Projects
Topic: Remember These?
Replies: 504
Views: 15891

Re: Remember These?

This is of course a serious problem with these kind of amps. Two reasons come to mind as given in these two articles: gassy tube, old and not being used for many years. Reconditioning might help. https://pa0fri.home.xs4all.nl/Lineairs/Tubes%20reconditioning/tube%20reconditioning.htm Solid state rect...
by Wolfgang
Tue Dec 11, 2018 4:23 pm
Forum: Everyones Projects
Topic: Remember These?
Replies: 504
Views: 15891

Re: Remember These?

Rozenblit uses zener diodes around the regulator for this reason. But they start conducting long before their break up values and it's audible. The TL783 is a HV reg. and should do of course much better than an LM317. If "arcing over" comes with sudden increase in current through the tube my protect...
by Wolfgang
Tue Dec 11, 2018 4:05 am
Forum: Everyones Projects
Topic: Remember These?
Replies: 504
Views: 15891

Re: Remember These?

... it has taken a bit of fine adjustment of feedback, tube dissipation and B+ values in order to optimize the amplifier for maximum output with the least distortion into my own particular speakers, and helpfully, optimizing the amp has not actually required giving the output tubes a thrashing. It ...
by Wolfgang
Thu Dec 06, 2018 3:47 pm
Forum: Everyones Projects
Topic: Remember These?
Replies: 504
Views: 15891

Re: Remember These?

I don't think it's the cost, Mike. It's because OTL needs a lot of output current and only few tubes can deliver high current/low impedance. And suitable tubes for OTL operation normally have very low mu. Nothing is really "efficient" with OTLs. The only thing a developer can do in order to make it ...
by Wolfgang
Wed Dec 05, 2018 3:35 pm
Forum: Everyones Projects
Topic: Remember These?
Replies: 504
Views: 15891

Re: Remember These?

After listening for a while with the 6SN7/6C33 OTL I tried to find reasons for the different sound compared to TS amps. The TS amps also use a cascaded grounded cathode input stage and still they all suffer from too much "brightness" in relation to a solid lower mids foundation. Or we could say that...
by Wolfgang
Tue Dec 04, 2018 7:39 pm
Forum: Everyones Projects
Topic: Remember These?
Replies: 504
Views: 15891

Re: Remember These?

How did you get to these results? Only by calculation or did you actually look at the output signal (scope, DMM) with an 8R dummy load connected?
Did you add already NFB?
I was playing already in my mind with ideas about this tube for OTL use.