EL84's in Simple SE w Pin Adapter

[Anchan]

Can an EL84, possibly an EL84M
Sovtek EL84M
be used in a Simple SE using a straight pin adapter?
THD YJUni EL84 to 6V6 Adapter.

My B+ is around 425V-430V using a 5AR4 rectifier. I was thinking of using a 5R4 to drop the voltage by 20-30V or so. I believe this would take me around 400V or so. The drop across the cathode resistor would probably another 20V or so, which leaves me with about 375V across the tube. I believe this gets me in the ballpark. I know about the lack of slow startup using the 5R4.

Does anyone see any issues with this??

[nic6paul]

I think you could build an adapter yourself. Not sure I would be forking over $90 for a socket saver and a 9pin socket. I have no comment on whether it will work or not but I think you could make the socket adapter yourself.

[tubelab.com]

I think you will be on the edge of meltdown. I have not tried the Sovtek EL84M, but the regular Sovtek EL84 will glow if fed 350 volts or so. I have tried quite a few different EL84 types in the Simple P-P and the best versions for high voltage use are the JJ's.

The EL84 will draw about half the current that a 6L6GC or EL34 will draw so your B+ will go up and the drop across the rectifier will be less. Also the cathode voltage is usually 12 or 13 volts.

The JJ's will eat 430 or more volts of B+ but get excited if the screen voltage goes above 340 or so. Some of the other EL84's won't even go that far.

I am not sure if the Yellow Jackets with current limiting built in would help or not, but for the price they charge, I'll never find out. I would be more tempted to buy a $45 power transformer that results in a 320 volt B+ voltage (Allied 6K56VG) and make my own adapter for a few bucks using the tube bases and sockets from AES.

I have a Simple SE using the Allied 6K56VG and I run 6V6's in it. It sounds nice. Two circuit changes are needed. The cathode resistors for the output tubes need to be reduced. (I think they are 270 ohms) and you need to jumper across the 10 K resistors feeding the CCS chips.

[Anchan]

Originally Posted by nic6paul

I think you could build an adapter yourself. Not sure I would be forking over $90 for a socket saver and a 9pin socket. I have no comment on whether it will work or not but I think you could make the socket adapter yourself.

Yeah, they are too expensive. My question was more about the voltages rather than the actual pin adapter itself.

[Ian444]

6P1P to 6V6 adaptors. Could probably do with built-in grid stoppers but works as is.

Probably no good for long term use...

[Ty_Bower]

Originally Posted by tubelab.com

The EL84 will draw about half the current that a 6L6GC or EL34 will draw so your B+ will go up and the drop across the rectifier will be less.

I would be more tempted to buy a $45 power transformer that results in a 320 volt B+ voltage (Allied 6K56VG).

Another option would be to add another filter choke in the power supply, just before C1. It required cutting a trace on the circuit board, but is otherwise a very simple modification. This dropped the B+ on my Simple SE from 455V down to 335V, which should be perfectly safe for EL84.

If I can scare up a couple 9 pin adapters, maybe I'll try out the EL84.

[Anchan]

Originally Posted by tubelab.com

I think you will be on the edge of meltdown. I have not tried the Sovtek EL84M, but the regular Sovtek EL84 will glow if fed 350 volts or so. I have tried quite a few different EL84 types in the Simple P-P and the best versions for high voltage use are the JJ's.

Good information. Thanks.

I am going to avoid any kind of modifications, radical surgery, or meltdown situations at the moment, and leave the amp as is. The amp sounds freaking great. But if I can take the thread on a slight tangent, here is what prompted my question:

So, I have 2 simple se's hooked up in PP. Some of you have seen the thread I started about it a while ago. I ended up going with JJ 6V6S tubes, and that is the ticket for sure.

I put the output of the amp on a scope, and ran a 200Hz (why 200, I don't know) sine wave through it. I can get about a 5.5V peak on the wave, before the wave gets distorted, and the harmonics really kick in. So thats almost 4W peak in triode mode with an 8 ohm speaker. I flicked the switch to UL, and assumed I would be able to clear 7 or 8V without distortion, but it does not work that way. 5.5V seems to be the threshold of distortion even in UL. It got me to wondering if the similarly power sized EL84 would do better in UL, netting me around the 8-10W or so I was expecting in PP. BTW, when I switching between UL and triode using the EL34's the power difference was quite clear.

Anyway, the way my amp is set up now is pretty much perfect for my speakers, so if more than a simple pin converter is necessary, this idea will stay as a thought experiment for now. Of course there are other ways to get more power, if I need it down the road, like EL34's in triode or UL, so I'm not going to sweat it. But my question about the 6V6S's topping out at 4W peak in UL is still curious to me. I would think I could get more.

[Ty_Bower]

It might be interesting to put your scope on the grid of the finals, and confirm the first stage isn't what's starting to distort. Though I'd be very surprised if it was, unless it's starved for voltage. With the B+ conditions you report, that should not be the case.

[Anchan]

Originally Posted by Ty_Bower

It might be interesting to put your scope on the grid of the finals, and confirm the first stage isn't what's starting to distort. Though I'd be very surprised if it was, unless it's starved for voltage. With the B+ conditions you report, that should not be the case.

This doesn't seem to be the problem, but is a reasonable suggestion for sure. But I did take some other measurements which are very interesting. This may turn into a lesson more about speakers rather than amps, or maybe a combination of both, but here's what I did.

There are 3 pics attached here- all are taken from the speaker terminals, and with amp in triode mode. The first is a beautiful 5V 200hz sine wave running into a 9 ohm (had only 9ohm on hand) dummy 25W resistor. The next pic is an almost as sexy 10V sine wave going into a resistor. The top of the wave begins to compress above 7V, but it still looks pretty nice.

The problem child is the third pic. It is the same 200Hz sine wave, about 5V going into the actual speakers. Harmonic content is pretty obvious, and the wave looks more like an iceburg or a mountain range than the original sine wave. The speakers used are Klipsch RF3-II. They have a sensitivity of around 98db, and are rated at around 150W. Is this some kind of damping factor issue?

Fortunately for my particular situation, normal listening is at about 2-3V peaks. Very loud listening nearly ear bleeding can be had at around 5V, so I am operating in the sweet spot of this amp. If I ever switched speakers I may have an issue, but its not a problem for me now. But I am very curious what others have to say.

[tubelab.com]

I am going to guess that your speakers are less than 8 ohms at 200 Hz. Every speaker system has an impedance VS frequency curve. Sometimes the manufacturer publishes it, sometimes they don't. Google couldn't find the graph for your speakers and it isn't on the Klipsch site either. My Yamahas are "8 ohms nominal" but vary from 6 ohms to 40 ohms across the audio range. You might try your test with a tone closer to 1KHz since that is where most manufacturers rate their speakers.