Ceriatone Forum

British Style => 18 Watt => Topic started by: viortisi on January 07, 2014, 04:29:02 AM

Title: 18W TMB EF86 first Test .....Please Help
Post by: viortisi on January 07, 2014, 04:29:02 AM
Hi all

I have finally completed to build a 18W TMB eF86, and I'm in the process of testing it ....and here we start with the problems...

I tried a shot and I notices the TMB chanel does not work at all, the EF86 sounds horrible and fade down.

I have been tested the connection several times and they looks right, but I can see some voltages that do not seems right to me.

With the tube rectifier and preamp in, all pot to zero I record an unbalanced Voltage at the two anode of the Phase inverter on the V2 - 12AX7.

Pin1      162V
Pin 2      76V
Pin 3&8  80V
Pin6      239V
Pin7       70V

As the circuit is symmetrical I expect a similar voltage between Pin 1 and Pin 6

And the same for Pin 2 and Pin 7 when both channels Volume are grounded

This is the schematic I have followed

I have checked, re-soldered and replaced all the anode and cathode resistors and capacitors but nothing change, and I have tried to swap the preamp tubes.

Please some help

Title: Re: 18W TMB EF86 first Test .....Please Help
Post by: wyatt on January 12, 2014, 09:20:17 PM
Been trying to think of an attack plan for a couple of days besides telling you you've probably made more than one mistake.

A better option has not arisen.

Nik provides ballpark voltages for amp his models in one handy Excel sheet...

You'll have to flip through the sheet tabs at the bottom until you get to the EF86.

Nothing thing to do is to meticulously blueprint ever connection and make sure you made a good solder joint  (cold solder joints are  gremlins that create a lot of hassles) and making sure you didn't short any thing.

Print out the layout AND schematic and check off each component as you check it's connection.

Pull the tubes and check the voltage from the High Tension (HT) winding at the rectifier socket as well as measuring all the heater/filament connections to make sure they are getting power. Put the rectifier in and make sure you're getting correct B+ voltage to the first filter cap. Insert power tubes and check voltages, insert preamp tubes and check voltages.

You can also research light bulb limiter and build one, to use FIRST and check to see it indicates a short somewhere in the power supply.

Title: Re: 18W TMB EF86 first Test .....Please Help
Post by: arledgesc on January 28, 2014, 11:09:55 AM
Some other things to check.  V2 10nF coupling caps can be leaky.  What is the B+ voltage measure feeding the two 100K plate resistors?   Also detailed pics would help.   It usually something constantly overlooked or assumed worked or was correct prior.  But on a new amp it can be anything until proven to work.   Broken wires, poor soldering, component out of tolerance, etc.

Title: Re: 18W TMB EF86 first Test .....Please Help
Post by: viortisi on January 31, 2014, 08:48:09 AM
Thanks for the recommendation ... I have been testing and testing the amp, finally with surprise I discovered that the board used for the Turret , is faulty; actually it is not isolating at all. I can measure an impedance between turret while they should be insulated.
I have been discussing with the supplier and hopefully I will get a replacement soon...

Now I have to rebuild ll the turret board...life!!

Will keep you updated


Title: Re: 18W TMB EF86 first Test .....Please Help
Post by: arledgesc on February 02, 2014, 11:12:23 AM
Good job!  Tube amps are such high impedance that it doesn't take much to be conductive and throw off the circuit.  I worked on an old amp once where a dust trail was conductive.  Birthing amps can be tedious.   2 out of 4 of mine had start up problems that were unique in some way.  And like you have been doing dig a little deeper and think outside the box.  But great job on hanging in there and not giving up.

Title: Re: 18W TMB EF86 first Test .....Please Help
Post by: viortisi on February 02, 2014, 06:11:09 PM
Hi all

while I wait for the new turret board , I would like to start the speaker cabinet.

Please do you have any recommendation on a good speaker suitable for the 18W tmb EF86..

Do I go for 1 or 2 x 12" cabinet?

Is any preferred speaker impedance? I'm using a mercury O18RS-FS that can accept 4-8-16 ohm.

How do i select the speaker power?
Suggestions are welcome

Title: Re: 18W TMB EF86 first Test .....Please Help
Post by: arledgesc on February 03, 2014, 08:11:26 AM
I just use an Avatar G212 traditional cabinet (open back) with a couple of Scumback 12" speakers.  The speakers are rated 60W each and 16 ohm each wired in parallel giving effectively 8 ohm load.  I use other higher power amps as well with these speakers but sound great with the 18Watter.  The cabinet was delivered with Celestion mix rated 30W and 60W respectively and sounded OK but a little rough on the top with any amp.  Not sure how the EF86 comes into play with your amp.  With EF86 you may prefer Alnico magnet speakers which heighten the upper end response and good for "clean" distortion.  Power wise a couple of 12" speakers in the 15 to 60W range should work.  Celestion Greenbacks @ 25W each may work as well as Celestion Alnico Blues @ 15W each.  The Blues are pricey though.   Anyway to 18W TMB responds well with two 12".  I can get controlled feedback easily with this amp and speaker combo.

I like buying 16 ohm speakers as they seem the most versatile.  Two in parallel yield 8 ohms or four in parallel yields 4 ohms.  I generally don't like wiring speakers in series like two 8 ohm speakers (8 + 8 = 16) as one could fail and you would have no sound.  Speakers usually open circuit when they fail electrically.

Title: Re: 18W TMB EF86 first Test .....Please Help
Post by: viortisi on February 05, 2014, 01:34:31 PM
Hi thanks for the useful information.

I'lo go for 2 of 16 ohm.it Is more versatile.

I have looked around on the web and I have seen the following  speakers

Now here I see very different types and prices...wondering if anyone can provide some feedback and if ever been used with a 18w tmn ef86

I like British sound and I use mostly distortion..any recommendation?

Title: Re: 18W TMB EF86 first Test .....Please Help
Post by: Interstellar50 on July 08, 2021, 12:03:44 AM
Thank you for good knowledge I've read a lot of useful information.

Title: Re: 18W TMB EF86 first Test .....Please Help
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