1-tube reverb-voltage

[adamG]

Hi Guys,

Could you advice me what tensions should be applied onto transformer and pin 6?
Recently, I assemble 124 with with 1-tube reverb.
On Fenders' schematics there's a figure of approx.400V (transformer) ,but I am afraid ,it is too high, right ? 

Thank you in advance.

Regards,

Adam   

[tubenit]

It will work with a wide range of voltages.  If possible, try something like 275v to 325v range.

With respect, Tubenit

[adamG]

Thank you T.
Is it the voltage on transformer?
How about PIN 6? This one is connected to next node via 100K resistor.

Regards,

Adam

[tubenit]

Yes, I was referring to the transformer voltage.  On pin 6 try 140-200v  range on plates so try a B+ node with 240-280v.


Honestly,  I have found a wide range of volts that worked to my satisfaction.

[PRR]

> it is too high, right ?

Wrong. That voltage into the transformer should be very high to get some current flowing in the puny 12AX7. Do not be afraid to go a bit past 400V. Yes, this "violates" the 12AX7's 330V max voltage, but many classic designs did that for many decades; the 300V-330V ratings are not hard numbers.

I would not expect it to work "well" with less than 300V maybe 250V. (It will "work" down to 100V but will not be strong and rich.)

I would feed it from the G2 Screen node of your B+ chain.

The node D pin 6 network is not critical except it should be clean. Typically you feed this from the same B+ node as your first stage(s).

[tubenit]

OK,  I actually looked up voltages on 7 amps that had a one tube reverb where I liked the reverb on it and thought it performed to my expectations.
It certainly wasn't "surf reverb" but I typically ran the reverb pot at around 3-4 max with these voltages.  And ran the dwell pot around 5-7 & I had all the reverb that I was wanting. 
   I don't have this measurement but it was 301 B+ with a 100k resistor to plate
251       I don't have this measurement but it was 251 B+ with a 100k resistor to plate

With respect, Tubenit

[adamG]

Thank you guys, very much!
I really like this forum.
Yesterday ,I adjusted voltages on preamp tubes. On reverb one, I have Pin 1-328V ,Pin 6-218, Pin 3-2,46V, Pin 8-1,6V.
Do you think ,it's ok?
Pin 1 is supplied from node D via add.2W resistor. Pin 6 i conn.to node E directly.
Anyway, I've got a plan for today to fire the amp up and I'll raport you what was going on

Regards,

Adam

[tubenit]

If you please provide an exact schematic of what you are building, it would be MUCH easier to answer your questions.

With respect, Tubenit

[adamG]

Actually, I work on 124 schematic att.to this topic with reverb stage as disscused above.
There's no FET, relays power 14V AC taken from separate tap on PT and its DC circuit after. 3-buttons FS via DIN socket into relays with solution of LEDs supplied by voltage drop across resistors 1,5K in FS box. Two inputs HI/LOW. 330p Mica caps on OD tube socket.   
HT via graetz bridge.
4 russian tubes 6N2P-EW with DPDT toggle to switch over 6,3/12,6V (for 12A_7/ECC) 
These russian tubes are very, very cheap and very good. Russians never economised expensive metals for tubes production! They cost in my place approx.2,5$ 
When I am ready, I'll release photos for this build and the right schematic.

Regards,

Adam

[tubenit]

Ah, OK ......... Dumblish 124 build.  Thanks for clarifying that.

The "one tube" reverb idea came from the D-style cloners on TAG.

Look forward to your photos and documentation.

With respect, Tubenit

[adamG]

Here is today's schematic.
Recently, I've struggled with the amp. I made two mistakes, corrected now.
Today, I need to swap Level pot that was broken or whatever.
Also, I'll take another try to lunch reverb.
So far, this 124 ver. is incredible!!! I love this circuit. Mr A.D. created a kind of magic. This is the Icon amp!
This is my third build of 124 50W. I am sure, I'll continue this amp buildings till I am alive...

Regards,

Adam

[adamG]

Guys,

Please, help!

After three-four days of struggle I got the amp working...without the reverb. It's still mute.
Here is the reverb board that is on top of the main one.
I attach it ,because maybe I made some stupid mistake?
Any sugestions?

Regards,

Adam

[tubenit]

Adam,

I am not able to understand what you've done by looking at the layout board.   The schematic that you drew looks correct to me and I don't see any mistakes in the schematic.

IF you check and post voltages on the triode plates and cathodes that might help?

My guess is that there is some simple wiring mistake that you will figure out and then have great reverb to add to the already great tone that you have.

Would it be possible for you to draw the layout board showing how wires hook up to components, pots and tubes?  That may help us help you. In your first post on this thread, you posted a picture of several layouts for the one tube reverb that showed the wiring to components.

with respect, Tubenit

[adamG]

Tubenit,

Probably, I found the error on my reverb board. While preparing its layout, I noticed that  
I just connected node E directly to 0.01 cap, not via 100K resistor...
Later on today, I'll check that on amp

Thank you very much!

I'll report you if I am successful.

Best regards,

Adam

[tubenit]

Look forward to your success!

[adamG]

Hi Guys,

Here it is...my success
Yesterday, I finished 124 ,at last.
I made three stupid mistakes. First, I put two resistors 2.2M on V1 as LFB, instead 22M. Those two were in the same foil bag...
Whole day I searched for that.
Second, I did not grounded DIN socket. When conn.to ground, the amp became recover after previous noise/hum.
Third, reverb did not response because I forgot to ground tank input
So now, the amp is as I dreamt. To me, it is the best one of all I built. I am happy with that.

When I am ready, I'll share photos and maybe sound clips ,also.

Thank you and best regards,

Adam

[adamG]

....also, my two cents to this thread...
http://el34world.com/Forum/index.php?topic=14348.msg135594#msg135594

To provide this solution of LEDs without plus pole it is necessary to change philosophy of relays, with is as follows IMO:
when NC contact is on the LED does not illuminate. It works for OD, because NC contact is off and then LED's circuit is on.
With PAB ,acc.to 124 schematic, the above is not possible, because its circuit is ( should be) activated together with LED's one. Relay's coil is on but LED's one is not. Check that in practice. Neverthless ,what you try. You won't be able to supply the LED together with switch. So, the positive pole is needed  for PAB.
I hope ,you'll decode what I wrote

Regards,

Adam
 

[eldredjames]

WHAT does PAB stand for on the above schematics?

[pompeiisneaks]

PreAmp Boost

[EL34]

EL34 edit:
This post by adam got corrupted somehow
I deleted it but copied the text and reposted it below

First ,"normal" position of PAB relay's contacts is NC. PAB is activated when NO ones are closed. Second, relay's coil circuit is closed by resistor and LED in FS box. In this way, PAB is permanently ON without possibility to turn it off by FS or/and by switch in an amp.
For OD relay it is possible to implement this system, because "normal" position of NO contacts is ON. So, you have clean stage ON. When the switch in amp is changed over, then the coil is off. The LED's circuit is activated.
So ,above means that NO contacts need to be used for PAB, instead of NC ones. But ,this also means reconection of other components ,IMO. 
I hope I described it properly    
Regards,
Adam

[adamG]

Hi Guys,

Recently, my 124 Reverb has been done.
Here are pictures of the amp chassis.
Within next days, I'll publish photos of the combo, as well.

Regards,

Adam

[tubenit]

Looks fantastic!  THANKS for sharing the photos.

With respect, Tubenit

[kagliostro]

Tubenit, I would like to know if you tried a different tube (not 12ax7) in the one tube reverb circuit

Thanks

Franco

[adamG]

I would like to know if you tried a different tube (not 12ax7) in the one tube reverb circuit

No, I did not, but that is a good question. You know, I'll try 12AT7.
Actually, I had a serious problem with 12AX7, which should be a NOS one, only.
Modern ones do not withstand voltage over 300V, IMO. I tested two of them and as said, NOS RFT and Tesla did their job ,only

Regards,

Adam

[adamG]

THANKS for sharing the photos.

Thank you T., very much!
I really like this amp and I dare to say, It is a great baby, worth of every effort.

Best regards,

Adam

[kagliostro]

The price is usually low, so, remaining on 12ax7 type, if you can find it, give a try to the russian 6N2P-EV (6Н2ПEВ)

Franco

[adamG]

...give a try to the russian 6N2P-EV (6Н2ПEВ)

I like above tubes very much, but they could not withstand the voltage over 300V ,unfortunately.
I provide them every time as I can. But for that solution ,they're not ok. For some moment 6N2P-EV worked, but suddenly stopped with no reverb.
So, I replaced them with NOS ECC83 and the problem is gone

Regards,

Adam

[tubenit]

Tubenit, I would like to know if you tried a different tube (not 12ax7) in the one tube reverb circuit

Yes, I have used a 12AT7 and a 5751 before.  They were OK.  Typically, I've used a 12AX7.

With respect, Tubenit

[kagliostro]

Thanks


Franco

[adamG]

To complete this topic, I publish the combo's pics.
I like this amp. It sounds warmly, softly, as good as I always dreamt about;)
For me, 124 is The number one.

Regards,

Adam

[tubenit]

That's beautiful!  What a great job.  Thanks for sharing the pictures.

With respect, Tubenit

[bnwitt]

Beautiful work Adam

[adamG]

Friends,

Thank you very much! I appreciate it.
These words of praise are very important for me.

Regards,

Adam