Oh my… I went through a whole year without an article on my website. This is embarrassing. From an article every few weeks to one whole year without any news?
I guess this is what it’s called “life happens”.
Also, there is another reason for this. As your system progresses, you eventually reach a point where it’s harder to get significant improvement. I’m not so interested in “lateral forays”, more interested in “vertical improvements”, if you get what I mean.
So in other words, no improvement, no news from me.
That said, I built this amp some time in July 2015 but I had problems with it. She sings but worse than the toad in me. I spent lots of time checking before I start to suspect it is the output transformers when I then packed her up and sent to my friend to debug and rewound the output transformer.
True enough, it’s the output transformers. Unfortunately the core can’t be re-utilized, hence it’s now a C core instead. I know, the looks isn’t that coherent anymore but looking at the bright side, my wizard friend wound up an awesome pair of output trans.
With new pipes, she sang fine as a lady but… not very exciting. Yeah, I’m a greedy bastard! Is this another case of “lateral foray”?
Ahem, This is where you earn your spurs!
Buoyed by my success with Schottkies in the Wet Dream project, I had the Schottkies installed and…
Boom! Crash! Bang! OMG!!!
Through the roof Expletive Factor!
What a huge improvement!
But then why am I surprised? I was thrilled before by what this little sand device could do, so the improvement wasn’t unexpected. What’s unexpected is it is as though she went from a lithe slim lady to a kick ass MMA fighter with a bod to match.
THE BASS. THE IMPACT. THE DYNAMICS. THE PRESENCE.
When these 3 attributes improve, everything else improved by a quantum leap.
As any experienced amp builder will tell you, the biggest bang for the buck is at the front stage. So opting for the Schottkies at the 5965 cathodes make perfect sense.
I then told my friend Tim about this new girl who caught my heart, and as I was describing the sound to her, particularly the kick ass bass and gut wrenching dynamics, Tim said, “Hey, sounds like a Gina to me.”
All is good so far but a new problem presents itself. My favourite 5965 tube is a GE 5 star. An absolutely rock solid tube but in current iteration of Gina, the sound is now a bit too forceful and tends to be harsh at peaks.
Yeah, I like foreplay, girl, but you are too rough! Foreplay doesn’t mean a broken finger or a sprained ankle, OK? One of these days, I may end up with a torn ligament for God’s sake…
That said, Gina is back to being a lady when Telefunken 5965s are used. But what good is an amp if she only sings with rare premium tubes?
Ahem… back to what I had in mind. My original vision of Gina uses TV damper diodes to provide slow turn on and I kinda like the brightness of TV damper diodes besides the other tubes.
“Slow turn on + Foreplay = Win Win”
But the TV damper diode was taken out when I was debugging the amp when it was distorting badly.
Now that the culprit’s been identified and replaced, it’s now time to put this fella back to work.
I’m using 6AX4 here as it’s an octal tube so if I hate it, I could easily mod for other octal tube type rectifiers. The slow turn on is a bonus.
And now we have a new Gina! No more of that harshness at peaks. No more of that “I will only behave if you give me Telefunken” attitude. The heft and dynamics seemed to have reduced a little, but I’m okay with this. After all, this is the MOST dynamic sound I’m getting out of my pair of horns right now. Chew on that!
Okay, about the schematic.
Gina can be built at a budget. And I mean it.
5965s, SV83s and 6AX4s are plentiful and still cheap. Before Gina, my favourite little pentode is the EL84. After dating Gina, SV83 is my true love. There is no contest here.
The SV83 or 6P15P is operated in a triode mode. The cathode RC combo and the triode mode connection are options for mods in future. But for now, Gina is very good to me.
Don’t be fooled by the looks of the 5965. Though touted as an 12AV7 equivalent, some folks have used it in circuits calling for 12AT7 etc. From my time with this tube (since the days of the Darling amp), I find this tube to be way better than the other 12A*7 brethrens.
6AX4 is such a nice approachable fella. Big glass, uses the common octal sockets, dirt cheap, low voltage drop (~10V with Gina), pretty bright and slow turn on of about 15 seconds… What more not to like of this fella?
Nothing special here but nowadays I stay away from electrolytics in the supply. I know the SV83 cathode electrolytic capacitor still influences the sound, so this may go one of these days but the usage of plastic caps in the power supply is recommended here. Hey, plastic works wonders on some girls right?
I didn’t specify grid stopper resistor value nor power transformer secondaries. These need to be adjusted for what you have in hand. You may not need any grid stopper resistor. My Gina needs them, as without them, there was some oscillation. Since this is a choke input supply, if you need to bump up the B+ a little, a small cap just before the first power supply choke will do.
Most amp builders will zoom in on the coupling capacitor here and tell you that you need to use boutique part here. That’s fine if that’s your preference but my Gina uses a USD2 Russian teflon capacitor. And I don’t feel inadequate in any way. And I have used various boutique caps before. But if you feel inadequate, by all means…
Gina above gives a glorious 2.3W to your speakers. Very efficient since she’s only flowing ~32mA. I recall I built a similar amp with a big honking pentode in octal sockets and even with the much higher current, it was only good for 1.5W. And not very good sound to boot.
There you have it.
Gina oh Gina!
She doesn’t need Telefunkens to shine.
So I could reserve this special tube for the special occasion.
Like when the real Gina comes knocking on my door.
Err, kicking it down is more like it. I’ll get the handcuffs ready…