Davoli Krundaal amp very old question refurbished - ELL80 tube substitutes

[kagliostro]

Many years ago (2007) one of the first question I submit here was about the replacement of the ELL80 tube on a Davoli Krundaal Power Unit (the UP50 version) (old italian guitar amp)

Now I'm here again with an inerent question

The schematic of the power section of the amp to which I refer is this



it uses as PI a double pentode ELL80 (connected as triode)

Davoli also did a less power version of the power unit that used an ECC82 as PI (the UP35 version)



As the ELL80 is difficult to be find and expensive since many years, some guy use a pair of EL95 as substitutes (a pair of EL95 is the same of an ELL80 but in a single bottle); also, a friend of mine, tried to use the ECC82 PI as in the UP35 version of the circuit but wasn't satisfied with it, so he developed a personal mod (that gived better results also in output power that was around 70W) using a 6CG7 tube





Now 6CG7 is not easy to be find for me, a bit easier (to me) is to find EL95 tubes but a single 6CG7 or a pair of EL95 will cost around 20€ (or more) (and also I can use the EL95 in a better way as power tube for small PP amp)

As I've enough ECC82 tubes that I got some years ago on the cheap I've think ....

copying the circuit of the PI of the UP35 version and using a pair of ECC82 with paralleled triodes instead of only one ECC82, will this pair of tubes give me the performance of the 6CG7 tube mod at a way less price ???

What do you think about ? Will it be feasible ??

Thanks

Franco

[shooter]

wasn't satisfied with it

so I understand;
you want to use 2 tubes, 4triodes?

is ecc82 ~ = to 12AU7 ?
If so, did your friend rebias the PI?  AU7's don't really like being "dropped in" as a direct swap.

[kagliostro]

Ciao Shooter

Yes, ECC82 = 12AU7, same tube only european version

The original circuit he was modding was the Davoli UP50 that used ELL80 tube as PI

he modified the connections to use the UP35 PI (on the UP50 circuit) that used the ECC82 tube as PI but he told the output was weak if compared to the output obtained using the ELL80 PI (remember we talk of the UP50 circuit on which was tried the UP35 ECC82 PI circuit))

so he modified the connections of the PCB of the UP50 (that used the ELL80 as PI) as to use a 6CG7 tube as PI (you can see the image of the PCB I posted) and this time the output increased and also rised over the original situation with the ELL80 PI

Yes, I'm asking if I can use 2 ECC82 (4 triodes) to obtain a virtual tube that will be stronger, it will cost me 4€ instead of 20€ or more (I've enough tubes of that kind in my stock)

Franco

[shooter]

we're on the same page 

he told the output was weak

If you're experimenting, I'd look through PI circuits that use AU7(ecc82) and start there with 1 tube. My limited PI knowledge wants to "think" you want a big and strong AC swing at the output more so than big current (parallel)   

[PRR]

Parallel 12AU7 may replace 6CG7.

I note that TAD sells 6CG7 for 29 Euro, and that avoids fitting two bottles.

"Feasible" and "satisfied" maybe two different things. It can work, and yet you not be totally satisfied.

(On the other hand: do you NEED a 60W-70W tube amp today?)

> My limited PI knowledge wants to "think" you want a big and strong AC swing at the output more so than big current (parallel)

You still have to drive the load. These are TV sweep tubes, not audio tubes. They may have high grid current. Krundaal wisely used low-value 33k grid resistors on the power tubes, so the bias is less likely to run-away when the tubes get hot. Using a 3:1 rule of thumb for voltage amplifier, a 30k grid resistor suggests 10k driver plate resistor and 3k driver plate resistance. One section 12AU7 is not there. Two sections parallel may be close.

Two EL84 as triode is interesting but a lot of heater power.

[PRR]

I know you want to use-up your bucket of 12AU7, but this is a big job for a medium size tube.

I was just reminded of ECC99.
http://www.mif.pg.gda.pl/homepages/frank/sheets/163/e/ECC899.pdf

A plot with 275V B+ and 10k plate resistors 33k grid resistors looks promising. But it is weak at pulling the "off" tube really off. I would consider shifting to higher current (lower plate voltage) by changing 390r to something lower, even 150r.

Ah.... TAD has ECC99 at €16.40 - BUT an excessive €19 delivery to Italy. (Planning a trip?)

[kagliostro]

Thanks Shooter & PRR

Sorry for the delay on the answer

yesterday my back got stuck and I'm using some very powerful painkillers (although with not optimal results) and that's why my mind isn't very clear

I hope I can go on with this conversation tomorrow, today my ideas are not enough polished

Franco

[shooter]

with not optimal results

been there.  Gave up moved to lots of chiropractic and physical therapy, tempered with some good home-grown beats the pharmaceuticals hands down 

[kagliostro]

been there

Sad that you know (in detail) what I'm saying

Franco

[shooter]

getting old is not for the faint of heart 
hang in there Franco, we may not be able to over come pain but we can lie to ourselves enough to ignore it 

[PRR]

I think you should switch from 60W tube amps to class D amps.

All of us who hoisted big tube amps in our youth know what your back feels like.

(Actually my back "feels" fine today; but there is a nerve pinch at L4L5 which makes me think my leg/knee hurts like hell, all the time. And my doc took me off good old Aspirin after an unrelated bleeding problem. Tylenol is like 3.2 beer- no kick.)

[kagliostro]

Hello Friends

Today is way better, not that I solved entirely the problem, but I can go up and down from the bed without pain and, if I'm careful, I can walk without pain (at the moment to be careful is a must or I feel something like a BIG Nail on my back, dont remember well but seems my problems are on 3L - 5L - two herniated discs)

Usually (every day) with my morning coffee I get 1000mg of Paracetamol & 1mg of cortisone (deformed arthrosis in the hands and tinnitus in the right ear)

this days I tried (with not much results on solving the pain) with Toradol (a very strong painkiller to be used very carefully that I used a pair of times and suspended) and Tachidol (500mg Paracetamol & 30mg codeine, here the use of codeine is downhearted because there was a time that drugged people used it as a droug) I think that the thing that give me the better result was the use of doses of 12.5mg of Prednisone (I've on my stock some Deltacortene 25mg pills a corticosteroid, this acts as an anti-inflammatory and not a pain reliever)

So, today, I can walk a little and feel only a small pain

PRR did you ever tried some anti-inflammatory (corticosteroid or not), the use of painkillers give help but didn't solves the problem

---

Well here we are with the Davoli

PRR Many thanks for your indications

You show me the plot about ECC99 a tube that I was considering but as you say at the end is no cheap

I wouldn't want to give you too much trouble, but, if you can

the 6CG7, from that point of view, how does it behave ?

(my friend years ago just tried on practically and no calculations about it)

(Here I think you referred to the ECC99) ....

But it is weak at pulling the "off" tube really off.

is the same for the 6CG7 ??

---

In the meantime I thought of a couple of possible alternatives to solve the problem (which is mainly of costs)

One solution:

I verified and the 6DL5 is a russian correspondent of the EL95 tube, so I'm looking if I can find it on the cheap (in Hungary via a Radio Amateur Friend), the same for the 6N6P (6Н6П) that corresponds to the ECC99 / E182CC

Other Solution:

This is a bit more complicated and involved again the use of a pair of tubes

Borrowed in some way here:

http://www.chambonino.com/construct/const9.html

http://www.chambonino.com/construct/constwire2.html

(this is something a guy proposed years ago as to solve the problem of the Davoli ELL80 PI also increasing power, but wasn't tried)





Thanks

EDIT:

I've one other "option" I've read that 6CG7 is the same of 6FQ7 and that 6FQ7 is the same of 6SN7 tube .... don't know if this is real, if it is I've some 6SN7 tubes, someone can confirm they are equivalent to the 6CG7 ?

Franco

[PRR]

> tried some anti-inflammatory (corticosteroid or not)

I had instant relief from a large injection of steroids in the emergency room. I could hardly walk in, but was able to walk well to X-ray and scans, went shopping that afternoon.

But I think a month of oral steroid is why my cataracts "bloomed" a few months later.

Paracetamol is sold as Tylenol here. Take too much and your liver falls out. I'd doing about 1/3rd of the "maximum" dose.

Yes, Codeine is very controlled here, it is an opiate, a weak form of Heroin. A friend uses it, but has to sign a log at the drug-store, and I think the State tracks those sales. A flood of low-price synthetic opiates (Oxycontin) has reduced the demand since my younger days, but all addicts know to find codeine if they can't get the strong stuff.

As you say, no drug fixes the problem. It may help you move and stretch more, which is the path to getting better again.

[kagliostro]

Ciao PRR

.... no drug fixes the problem. It may help you move and stretch more, which is the path to getting better again.

Yes, that is right

Unfortunately today the weather isn't good and so my back, yesterday was a better day, I was able also to go to my laboratory and do some things I promised to my son

Franco

[kagliostro]

Reading here

http://www.fourwater.com/files/hist6sn7.txt

I see confirmed that 6SN7 tube is the same of  6CG7 tube (or better, they are the same of the 6FQ7 because of the schield that is present on the 6CG7) and luckily I've some 6SN7 and 6Н8С (6N8S), the russian version

the 6SN7 has a heater consumption of 600mA, only 50mA more than the original ELL80

So I think I can use those to drive the EL500 - EL504 tubes

(I was starting to think of using EL90 tubes that I got on the cheap some time ago, but I hated using it as PI as disliked to use the EL95, also if I've some EL90 and only few EL95)

Franco

[PRR]

Yes, most of the Mu=20 triodes are very very similar, differing in plate and heater ratings.

That page gets some things backward. The grand-father is the 6J7, a great pentode. With extra grids omitted it is the 6J5. Then the twin-6J5 with top cap is the 6F8; without topcap the 6SN7, with Loctal equivalents.

12AU7 is the same idea but smaller. This gives different ratings and the curves are not quite the same. There are several other miniatures with different ratings. So many that numbers started to overlap and one tube can carry two numbers.

All these tubes were made many places at different prices so there is some variation. Certainly enough to start arguments in golden-ear forums. For driving a guitar amp, the higher plate rating is more important than the curves.

[kagliostro]

I had instant relief from a large injection of steroids in the emergency room. I could hardly walk in, but was able to walk well to X-ray and scans, went shopping that afternoon.

Honestly, I fear intramuscular injections, you can make me an intravenous injection, an IV or any puncture in the mouth, but I fear the intramuscular ones

this is due to something happened when I was young, when the injections were made with recycled materials, glass syringes and re-used needles, boiled in a special container with the intent to disinfect them

But this morning I asked to my wife and got 4mg cortisone via an intramuscular injection
(with a discreet result, since I could not sleep tonight)

---

Back to the ELL80 substitutes

A friend give me an idea for an alternative
(a tube I can find not everywere but I can have on the cheap)

As I'm not able to figure by myself if the substitution is feasible, please can someone give a look and say what he think about ? (Thanks)

QQE03/12

https://frank.pocnet.net/sheets/030/q/QQE03-12.pdf

http://frank.yueksel.org/sheets/143/q/QQE03-12.pdf

https://frank.pocnet.net/sheets/183/q/QQE03-12.pdf

http://tdsl.duncanamps.com/pdf/vm298.pdf

ELL80

http://www.r-type.org/pdfs/ell80.pdf

http://oldradio.qrz.ru/tubes/foreign/02/ELL80.gif

http://oldradio.qrz.ru/tubes/foreign/01/ELL80.gif

https://frank.pocnet.net/sheets/201/6/6HU8.pdf

https://frank.pocnet.net/sheets/124/e/ELL80.pdf

ELL80


QQE03/12



---


About the use of the QQE03/12 as PP Power Section, I'm sure it is feasible, our friend Darryl build an amp that way


(the Brisk4 - that uses GU17 tubes = to QQE03/12)





But here (on the Davoli UP50) there is also to connect the pentode in triode mode ..... really confused, G2 and cathode on QQE03/12 are internally joined   




MANY THANKS

EDIT: Looking around I've find this Pentode LTPI



But, is late and my brain didn't want to help me to understand if this will of some help to understand if I can use the QQE03/12 as PI in the Davoli UP50 (also if seems that on the Harman Kardon schematic G2 are connected together and the same G3) 

Franco

[PRR]

> G2 and cathode on QQE03/12 are internally joined   

I do not see that. There are two G2 (for the two sides), connected together. There is no G3 shown; it may be a true tetrode, it may have a G3 or side-rods connected to cathode, it may be a critical distance tube where a G3 "effect" happens with geometry and spacing.

The Harman Kardon plan uses 6550 which do not have G3 pinned-out. I believe 6550 is a side-rod tube like 6L6 and the rods are internally connected to cathode.

G3 (or side-rods) have very little effect except in Pentode mode. With just plate and G2 we get dippy kinky curves. A G3 or similar at a low voltage masks this effect.

[kagliostro]

Many Thanks PRR

G2 and cathode on QQE03/12 are internally joined

my fault

I tried to say something and told a different thing

What I wanted to say is that there are two G2s but they are internally connected together and there is only one cathode (or two catodes joined) for the two tetrodes

--

it is a tetrode and as far as I can know there is no G3, I think there are side-rods as you say

--

about the Harman Kardon I was pointing the attention to the 12BY7A tubes of the Phase Inverter, not to the 6550 of the Power Section but I think you talk about the 6550 as to explain me about the low  importance of the side-rods except in pentode mode

--

With just plate and G2 we get dippy kinky curves. A G3 or similar at a low voltage masks this effect.

Here I'm missing something in translation

Please, can you explain with other words ?

I understand only that there is something that will go wrong but a low voltage can mitigate the effect (low voltage ... how much low ????)


--


BTW, I'm still not sure about the kind of PI the UP50 unit uses, is it a paraphase ?

Thanks Again

Franco

[PRR]

> explain with other words ?

Picture?


With no G3 effect (Tetrode mode), at low plate voltages the smooth curves get very not-smooth. With some grid or rods or distance between G2 and plate (Pentode mode), giving a near-Cathode potential in G2-P space, the curves smooth out.

> kind of PI the UP50 unit uses, is it a paraphase ?

I think so, but the grid-divider values look very odd. You should check if they really give equal-but-opposite outputs from the driver plates.

[kagliostro]

Thanks Again My Friend

now it's clearer


Franco

[kagliostro]

At this point I think the idea of QQE03/12 is to be abandoned in favour of other solutions

a 6SN7 tube wired as the 6CG7 of my friend or a circuit with a pair of tubes like in the example I posted



--

I've draw the PI hoping that the schematic is more clear and is possible to confirm or not if it is a Paraphase PI



Thanks

Franco

[PRR]

> it is a Paraphase PI

It is..... but one value is wrong. In a likely way.

We expect the voltage divider from plate 1 to grid 2 to un-do the gain of tube 2. But the values on your re-draws, 37k:33k, divide to about half, and we expect a gain near ten or fifteen.

And sim says 37k:33k gave very unbalanced outputs. Even if I raised "37k" to 137k.

I realized that 3.3k on the bottom was a very likely transcription error, and gave loss of about the right size. Right away the sim gave a near-perfect balance, and exact balance would be well within the range of the trim.

[PRR]

I am used to squinting at old plans passed through fax or copiers which "lose dots".

I realize that Davoli used comma, not dot, and the comma is very clear on "5,6k". So maybe a mistake in the original drawing.

[kagliostro]

Thanks PRR

May be it is late for me (here is 03:48 AM)

the wrong value is 33K and the right value is 3.3K, correct ?

This can be deducted also looking to the UP35 version (schematic on my first post that uses ECC82 as PI) where there is no trimmer but there is a 33K resistor and a 2.7K resistor (or not ?)

You are right, here we use comma instead of point to indicate decimal numbers

--

So it is confirmed, a Paraphase

--

Looking around for kinds of PI I've seen one that remember in some way the circuit that feeds the grid of the power tube via the cathode (schematic on my previous post)

the Isodyne PI, I've never seen something like that before    (with the bias part)

https://www.bonavolta.ch/hobby/en/audio/split.htm#Isodyne



interesting

Thanks again for all

Franco

[kagliostro]

To confirm PRR

I've find that in the UP 100 B Power Unit the resistor is exactly 3.3K as per PRR calculation



Franco