My dad recently gave me an old Teisco amp of his and I have been trying to find the proper power tube replacements for it. It originally came with two 7189A's, but I've been told that those are no longer in production. I have been trying to find a pair of Sovtel EL84M tubes to replace the 7189A's, but I have had no luck. I bought a pair of Sovtek EL84M's from Tube Depot, but had no luck with those because they got way too hot. Does anyone have any suggestions on where I can find the Sovtel EL84M tubes? Any help would be much appreciated! Thanks in advance!
I can't advise where to find the tubes, but maybe it would be better to modify the circuit to make it accept any EL84.
Re-biasing should do the trick. If cathode bias is used, you could increase the resistor values. Don't forget to check the voltage rating of the bypass cap
.
If grid bias is used, it's just an adjustment.
Do you know what class it runs in at present?
Re-biasing should do the trick. If cathode bias is used, you could increase the resistor values. Don't forget to check the voltage rating of the bypass cap
. If grid bias is used, it's just an adjustment.
Do you know what class it runs in at present?
Not sure I understand what you are asking.
Unless it is a typo, there is no Sovtel. Sovtek is the tube maker, and the only one I know making EL84M.
You can rarely make a tube type switch and not have to change the biasing. if EL84s are runnning red hot, they are biased wrong. Either the cathode resistor is wrong or the fixed bias supply is wrong, depending upon which you have.
And what B+ voltage are they running at?
Unless it is a typo, there is no Sovtel. Sovtek is the tube maker, and the only one I know making EL84M.
You can rarely make a tube type switch and not have to change the biasing. if EL84s are runnning red hot, they are biased wrong. Either the cathode resistor is wrong or the fixed bias supply is wrong, depending upon which you have.
And what B+ voltage are they running at?
The 7189 has a higher plate voltage rating than a EL84 or a 6BQ5. If the amplifier operates at 325 volts or higher, most of the EL84 variants will have a short unhappy life. The EL84 is rated at 300 volts max, the 7189 can take 400. The 7189A is an improved 7189 with even higher ratings. Some are rated as high as 440 volts.
The 7189 may be out of production, but they can be found on the internet. Triode Electronics sells several tubes that claim to replace 7189's but I have not tried them, they are cheap. Call them and ask if they will work for you. I found 7189A's available at Antique Electronics, but they are expensive, $42 each.
The 7189 may be out of production, but they can be found on the internet. Triode Electronics sells several tubes that claim to replace 7189's but I have not tried them, they are cheap. Call them and ask if they will work for you. I found 7189A's available at Antique Electronics, but they are expensive, $42 each.
The people at Eurotubes have new products and new old stock on the hard to find tubes. They can cross reference anything and are extremely helpful. They sell online and ship priority mail / insured....you'll have them in three days or less. Tell them that Hoyt sent you. It won't get you a discount but they'll like it.
Thanks for the help and suggestions everyone. I was told by someone who I thought to be a reliable source that there was an actual brand called Sovtel (not to be confused with Sovtek) that made EL84M's that could accept such high plate voltages and that there was a difference between the two brands and how they are made. I had never heard of a brand called Sovtel and just assumed that the Sovteks could do the job because they are military grade and are made to accept higher voltages. The person who gave me the information must have just made a typo in their e-mail to me. I suppose I will just have to get the amp rebiased or track down some NOS 7189A's. Thank you for the help everyone and sorry if any of this information has been confusing. I am a complete newbie to all of this and am trying to learn all I can.
I wonder if he means these:
http://data.gstube.com/?mmm=104
Some data sheets show the max anode voltage as 500 volts, this one with the curious stipulation 'closed tube'. They're easily available on e-bay, I bought sixteen 6n14n-eb recently for ~$45 USD. Sorry, don't remember from whom. The printed datasheet I have specifies an anode voltage range from 300-500 as well.
It should be noted the construction is completely different than Sovtek above the top mica retainer, but near identical below. FWIW I like them a lot.
http://data.gstube.com/?mmm=104
Some data sheets show the max anode voltage as 500 volts, this one with the curious stipulation 'closed tube'. They're easily available on e-bay, I bought sixteen 6n14n-eb recently for ~$45 USD. Sorry, don't remember from whom. The printed datasheet I have specifies an anode voltage range from 300-500 as well.
It should be noted the construction is completely different than Sovtek above the top mica retainer, but near identical below. FWIW I like them a lot.
For the last 25 or so years there has only been 5 or 6 mfgrs. of vaccuum tubes in the entire world. Whatever they're called it came from one of them...they private lable for everybody including GE. As tubes get old the printing on them oxidizes from the heat cycles and rubs off easily, making the "l" a"K" and SOVTEK is the winner.
I agree with the other guy....The sound gets right when you make the tubes sweat, so crank it, cook em and enjoy the sweetnes of tube sound. I like to use the most powerful tube that will fit in the socket and www.eurotubes.com has every cross over number to brand from years past that you could ever want. If I remember right they have a line on an defunct, old family electronics store and a couple of thousand origional tubes got liquidated reciently. Maybe there's a couple of 7189a(s) in there.
New tubes need to go through a few heat cycles until they settle down and you can smell them when you they work so don't be afraid. Sovteks are used by amp mfgrs. because they are cheap, plentiful and do the job. If you were to look at the botique amp mfgrs. you'll find the more top end tubes with gold plating and tighter tolerances giving you a nicer sound and a little longevity but still change them in a year if you want the best sound from your unit.
Crank it up!
I agree with the other guy....The sound gets right when you make the tubes sweat, so crank it, cook em and enjoy the sweetnes of tube sound. I like to use the most powerful tube that will fit in the socket and www.eurotubes.com has every cross over number to brand from years past that you could ever want. If I remember right they have a line on an defunct, old family electronics store and a couple of thousand origional tubes got liquidated reciently. Maybe there's a couple of 7189a(s) in there.
New tubes need to go through a few heat cycles until they settle down and you can smell them when you they work so don't be afraid. Sovteks are used by amp mfgrs. because they are cheap, plentiful and do the job. If you were to look at the botique amp mfgrs. you'll find the more top end tubes with gold plating and tighter tolerances giving you a nicer sound and a little longevity but still change them in a year if you want the best sound from your unit.
Crank it up!
7189A to EL84M: Is rewiring needed?
I'm trying to get a Bell 2440 integrated amp (4 x 7189A, plate voltage is 420) up and running. I put in a quad of Sovtek EL84Ms, but after the variac gets much above 100VAC the tubes start running away.
I've heard conflicting advice as to whether an amp calling for 7189A needs the tube sockets rewired to accept EL84M...anyone have a definitive answer?
Also, a tech recommended installing a bias trim pot (the bias is fixed but non-adjustable). The schemo wants -19 (and the tubes are currently getting -18) and I'm hoping that bringing that down (I should say, making the bias voltage more positive) will get the tubes under control (I may also add a dropping resistor to the power supply to try and shave off a few volts there. If anyone has any further suggestions, I'm all ears!
Thanks,
Seth
I'm trying to get a Bell 2440 integrated amp (4 x 7189A, plate voltage is 420) up and running. I put in a quad of Sovtek EL84Ms, but after the variac gets much above 100VAC the tubes start running away.
I've heard conflicting advice as to whether an amp calling for 7189A needs the tube sockets rewired to accept EL84M...anyone have a definitive answer?
Also, a tech recommended installing a bias trim pot (the bias is fixed but non-adjustable). The schemo wants -19 (and the tubes are currently getting -18) and I'm hoping that bringing that down (I should say, making the bias voltage more positive) will get the tubes under control (I may also add a dropping resistor to the power supply to try and shave off a few volts there. If anyone has any further suggestions, I'm all ears!
Thanks,
Seth
Re: 7189A to EL84M: Is rewiring needed?
The 7189A has pins 1 and 2 connected internally. The Reflektor 6p14p-ev (aka, Sovtek EL84M) has the control grid on pin 2, and pin 1 is not connected. Check the tube socket of the amp carefully. If the input signal goes to pin 1 and there is nothing on pin 2, then you must re-wire before the EL84M is going to work. I've heard of two occurrences of this now...
slor said:
The 7189A has pins 1 and 2 connected internally. The Reflektor 6p14p-ev (aka, Sovtek EL84M) has the control grid on pin 2, and pin 1 is not connected. Check the tube socket of the amp carefully. If the input signal goes to pin 1 and there is nothing on pin 2, then you must re-wire before the EL84M is going to work. I've heard of two occurrences of this now...
Yes, the grid must be kept at a lower voltage than the cathode. If the cathode is at ground, as it usually would be in a fixed bias amplifier, you need to apply a negative voltage to the grid. The more negative voltage applied, the less the tubes will conduct (and "run away").
At 420 volts on the plate, I'd say you should keep the overall tube current under 28 mA. If the schematic shows -19 volts bias voltage, they must have been running the screens mighty hard. Those poor tubes.
Maybe Kevin will chime in. I think he has an 7189A amp that ran in this territory.
At 420 volts on the plate, I'd say you should keep the overall tube current under 28 mA. If the schematic shows -19 volts bias voltage, they must have been running the screens mighty hard. Those poor tubes.
Maybe Kevin will chime in. I think he has an 7189A amp that ran in this territory.
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