Rocky - The Quatroquel

Mike H · Post by **Mike H** » Fri Jun 11, 2010 2:55 pm

Appendix ~ you could have a 10M45S CCS on the 1st stage anode if you want

pre65 · Post by **pre65** » Fri Jun 11, 2010 2:58 pm

Mike H wrote:Appendix ~ you could have a 10M45S CCS on the 1st stage anode if you want

Still got a couple in stock, in fact both chassis have one in position, would be a shame to take them out.

Just off to the machine shop (garage) to make some adaptors so I can use octal bases in a septar size hole.

Mike H · Post by **Mike H** » Fri Jun 11, 2010 3:07 pm

Awlrighty then, stay they will.

little eddy · Post by **little eddy** » Fri Jun 11, 2010 11:50 pm

pre65 wrote:Here is a better copy of the drawn circuit.

Phil,

That was my proposed schematic when I knew even less than I know now. Nevertheless nothing much has changed, (maybe I haven't learnt too much). Attached is the current version.

p.s. I find it very confusing when someone else is also called Mike H!

pre65 · Post by **pre65** » Sat Jun 12, 2010 12:04 am

So, is little Eddie really Mike ?

In the space of a day the design has moved on, and now Mike Holmes is looking at a design using 6DN7 as a cathode follower with an anode CCS and a grid bias choke on the output valve.

I am really looking forward to seeing what he comes up with. As it's so different to what you (and others) have done I have started a separate thread.

Mike H · Post by **Mike H** » Sat Jun 12, 2010 2:05 pm

pre65 wrote:So, is little Eddie really Mike ?

NO!!

In the space of a day the design has moved on, and now Mike Holmes is looking at a design using 6SN7 as a cathode follower with an anode CCS and a grid bias choke on the output valve.

No I wasn't, I was thinking about 6DN7, unit 1 as 1st stage, unit 2 as CF, with choke load. CCS on 1st stage anode.

@ Little Eddy SRPP is what he was using before I believe, I think the idea is to try summat different for a change. Is all.

pre65 · Post by **pre65** » Sat Jun 12, 2010 2:39 pm

Mike H wrote: No I wasn't, I was thinking about 6DN7, unit 1 as 1st stage, unit 2 as CF, with choke load. CCS on 1st stage anode.

Sorry, I meant 6DN7.

Mike H · Post by **Mike H** » Sat Jun 12, 2010 2:42 pm

OK I wondered if it were a typo!

Will be looking at it shortly, watch this space.

Well you've probably got time to make a cup of tea, walk the dog, have a nap ....

pre65 · Post by **pre65** » Sat Jun 12, 2010 2:43 pm

Mike H wrote:OK I wondered if it were a typo!

Will be looking at it shortly, watch this space.

Well you've probably got time to make a cup of tea, walk the dog, have a nap ....

Don't forget I have started another thread for the new version.

Mike H · Post by **Mike H** » Sat Jun 12, 2010 2:45 pm

Oh right so you have.

Will try to remember

little eddy · Post by **little eddy** » Fri May 10, 2013 8:12 pm

Now that my DAC is complete and I can think again about my ALAIT thread, (801a A2), I have been thumbing through a John Ranking book loaned by Nick.

He definitely has firmly held views on many aspects of amp design including quite a bit about driver requirements and circuits. He seems to like mu-followers and SRPP as combined gain stages and drivers which I though of interest, especially as he seems to favour the 6SN7 as I use in my Rocky amp in SRPP config.

1. Higher current - His recommendation is to drive a pair of parallel triodes at 10mA each whereas my Rocky has an Iq or some 7mA.

2. Max out Va - He also biases valves quite high at say 8V thereby having quite high Va for each triode, (circa 250V compared to my current 150V). He aims for 9dB headspace from the driver, 6dB being adequate.

3. Film cap at as an extra filter stage at the end of buffer voltage reduction network.

So why have my SRPP running with a supply of around 300V when I might manage say 380V. At 10mA I can probably get a Va of close to 185V per triode compared to circa 150V. He recommends driving valves hard at 90% of rating but I don't have the B+ 500+ volts necessary so would only be able to manage 4.5V max Vgk.

Does anyone have any views or experience on this as I thought any learnings might be useful when I get to the ALAIT build. Not much to loose.

If this works, might even be able to consider a 2A3 in place of the KT66, another valve he favours strongly.

little eddy · Post by **little eddy** » Sun May 12, 2013 6:38 pm

When you have something like the 6SN7 in SRPP, I am interested in the limitations and the use of heater elevation.

For the 6SN7 I have seen:

"heater +ve to cathode DC 100V, total DC and peak 200V"

So I propose I increase the bias to 100V (or 1/4 of B+ @ 400V max) and this part should be OK for the bottom triode.

Also "heater -ve to cathode, DC 100V, total DC and peak 200V"

So if I do elevate the heater to 100V, the peak output from the top triode could be 300V peak.

If I run the SRPP at say 10mA and Vgk of 4V, it looks unlikely the Va of the top valve will fall below 100V, so in theory the output should not peak above 300V with a B+ of 400V????????????

Also I previously used the same 60V heater elevation shared with the EL34/KT66. Are these valves OK with a heater elevation of 100V as the specs don't appear to state anything on this?

Am I at risk of blowing things up or is my logic OK?

ed · Post by ed » Sun May 12, 2013 8:33 pm

little eddy wrote:
Does anyone have any views or experience on this as I thought any learnings might be useful when I get to the ALAIT build. Not much to loose.

don't know if this is of any interest:

http://www.vitalstates.org/diy/amplifie ... 0SE%20srpp

little eddy · Post by **little eddy** » Sun May 12, 2013 11:29 pm

Ed,

Thanks for the link to the SRPP article which I recall seeing a long time ago and remember the suggested optimal relationship between Rk and Rload.

This suggests that you can optimise the load, I would assume by changing Rg of the following stage. But this relationship is mostly independent on the B+. Yes Rk is a factor and guess ra increases slightly as I increase Va, but largely if I increase or decrease B+, the optimum loading should be little different.

So if Rankin's recommendation to maximise the headspace of the driver stage whilst running at a healthy current has some benefit, I could try it quite easily. But just as per my second post, I wanted to check that I'm not going to exceed any limits of my current set-up and components.

With me using the EL34/KT66, I have circa 100V more of B+ available than if I had used 2A3 or 300B etc. so why not use this if it improves the driving capability of the employed SRPP stage.

little eddy · Post by **little eddy** » Sat Sep 20, 2014 1:35 pm

Owston is nearly upon us again so once again a desperate attempt to try and show something new.

Not that new really but inspired by Steve's 41MP/PX25 amp a couple of years ago, and me chickening out of trying a class A2 build, the plan is to morph the old Rocky amp towards something resembling Steve creation.

1st step is the 41MPs. I'm really happy with Rocky as it sounds so am nervous about stripping out the old SRPP 6SN7 stage before listening to the 41MPs. Not sure how much I'll get done for Owston but here goes.....

Initially I'm going to use a 10M45 CCS running at 20mA as this will allow me to test/listen without altering the supply voltage, just means it will have to dissipate around 3W per channel. I'll also have a switch on the front for the HT so should be fairly easy to switch between the two valve types.

I have a couple of more of Andrew's DC supplies to install so will have both 6.3 and 4V supplies for a while.

A couple of early pics attached.

Capacitor coupled to the second stage for the moment. If it all works, 41MPs will be moved to the front and interstage txs will cover up the holes vacated by the temporary sockets.

audio-talk

Rocky - The Quatroquel

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