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Vintage threads from the first ten years

AMPEREX EL-34...vs...SVETLANA

11/8/1999 4:07 PM
Fj	AMPEREX EL-34...vs...SVETLANA I have a pair of AMPEREX "bugler" EL-34's... my Marshall 50 watter ('76 2204, mark 2) was "biased" for the Svetlana 34's...I stuck the Amperex's in & sound was just fabulous!...I'm presuming that the Amperex's (for that short time I had 'em in-there) were NOT damaged because I didn't "re-bias"...are these old Amperex's able to withstand same voltage, current, as the newer Svets?...the buglers (in comparison) were a LOT less schrill, a LOT fatter, & harmonics just fired off the walls!...WOW!...hope I didn't hurt them w / out re'biasing 1st...?

11/8/1999 4:07 PM

AMPEREX EL-34...vs...SVETLANA

I have a pair of AMPEREX "bugler" EL-34's... my Marshall 50 watter ('76 2204, mark 2) was "biased" for the Svetlana 34's...I stuck the Amperex's in & sound was just fabulous!...I'm presuming that the Amperex's (for that short time I had 'em in-there) were NOT damaged because I didn't "re-bias"...are these old Amperex's able to withstand same voltage, current, as the newer Svets?...the buglers (in comparison) were a LOT less schrill, a LOT fatter, & harmonics just fired off the walls!...WOW!...hope I didn't hurt them w / out re'biasing 1st...?

11/8/1999 4:29 PM
Doc	The early Mullard and Amperex EL34s are the genuine article. They will withstand the highest anode to cathode voltage, screen grid dissipation, and plate dissipation of any the EL34 designs, and sound great in a hifi circuit (what they were designed for) or a guitar amp full tilt. Other types are just economical copies, using lower quality materials and construction shortcuts. In my opinion, the Svetlanas are the all around best made of today's offerings. Marshall amps were originally (subsequent to the early "bassman" copy) built around the real Mullard EL34 tubes. Problems with output tubes started when these premium tubes (and similar Amperexes) were no longer available as an OEM component. I don't want to start a "which EL34 sounds best" thread here. Some that actually have the nicest sound (for example Siemans) won't take the Marshall circuit punishment. The Mullards & Amperexes had it all. Take a good look inside your Amperex, through any vent holes in the plate structure. The grids should be gold plated.

11/8/1999 4:29 PM

Doc

The early Mullard and Amperex EL34s are the genuine article. They will withstand the highest anode to cathode voltage, screen grid dissipation, and plate dissipation of any the EL34 designs, and sound great in a hifi circuit (what they were designed for) or a guitar amp full tilt. Other types are just economical copies, using lower quality materials and construction shortcuts. In my opinion, the Svetlanas are the all around best made of today's offerings.

Marshall amps were originally (subsequent to the early "bassman" copy) built around the real Mullard EL34 tubes. Problems with output tubes started when these premium tubes (and similar Amperexes) were no longer available as an OEM component.

I don't want to start a "which EL34 sounds best" thread here. Some that actually have the nicest sound (for example Siemans) won't take the Marshall circuit punishment. The Mullards & Amperexes had it all. Take a good look inside your Amperex, through any vent holes in the plate structure. The grids should be gold plated.

11/9/1999 3:37 AM
Fj	I thank-you for your response Doc, I have adjusted the bias trim pot to read -30 on pin # 5...Is that a reasonable "re-adjustment" for the Amperex's?...should I further fine-tune the current adjustment for these tubes?...I'm tellin' ya', the difference in TONE is absolutely astonishing!...the Svets in comparison sound like I was playing thru cheap car speakers!...really!...

11/9/1999 4:41 PM
Doc	It's impossible to tell where the tube's bias current is set with only a measurement of the negative bias voltage on the control grid. It's kind of like the one-armed fisherman holdink out his arm and claiming he caught a fish "this big". To know where the tubes are running, you need to find the idling current and reference that to the plate voltage, to know the idling power dissipation. In the case of your amp, the Amperex tubes you've plugged in may very well be idling in a safe range now, but you need to verify that there is no overheating (turning from the black/gray to a brown/red/or orange) of the plate structure, both at idle (no signal) and at full playing volume. If the tube's plate color does not change from the normal cold, out of the box color, and the amp sounds great to you, then the tubes are biased somewhere within the optimum range. You can experiment with the bias adjustment, using your ears for listening and your eyes to carefully monitor the plate color. I would adjust the grid voltage by no more than 1.0 volts at a time. Making the voltage more negative will reduce perceived sonic warmth, which of course is ok for the tubes' safety. Lowering the bias voltage absolute value will allow the tubes to run hotter, sound warmer at lower volume settings, but could allow unsafe dissipation when the tubes are run hard. If the amp were mine, I'd set the idling current to run as low as possible, cosistent with good tone from the amp. This will satisfy the guitar player in you, and help keep those great tubes healthy for a long time for you to enjoy. There are some excellent tech articles and FAQs on this subject, posted on a few websites devoted to tubes and tone. If you haven't gotten to read some (and copy for future reference), you owe it to yourself to start. There are various ways to either directly measure the power tube idling current, or using an Ohm's Law algorithm, be able to infer what the current is by reading a voltage drop across a strategically placed resistor or using the output transformer primary as a shunt. You may already be versed in this stuff, so if you are, please don't take offense to the suggestion. Just wondering, do your EL34s have a short base with a metal ring crimped around, or a typical brown or black full height bakelite skirt? The older versions with the metal ring were built to take abuse. Doc

11/9/1999 4:41 PM

Doc

It's impossible to tell where the tube's bias current is set with only a measurement of the negative bias voltage on the control grid. It's kind of like the one-armed fisherman holdink out his arm and claiming he caught a fish "this big". To know where the tubes are running, you need to find the idling current and reference that to the plate voltage, to know the idling power dissipation.

In the case of your amp, the Amperex tubes you've plugged in may very well be idling in a safe range now, but you need to verify that there is no overheating (turning from the black/gray to a brown/red/or orange) of the plate structure, both at idle (no signal) *and* at full playing volume. If the tube's plate color does not change from the normal cold, out of the box color, and the amp sounds great to you, then the tubes are biased somewhere within the optimum range. You can experiment with the bias adjustment, using your ears for listening and your eyes to carefully monitor the plate color. I would adjust the grid voltage by no more than 1.0 volts at a time. Making the voltage more negative will reduce perceived sonic warmth, which of course is ok for the tubes' safety. Lowering the bias voltage absolute value will allow the tubes to run hotter, sound warmer at lower volume settings, but could allow unsafe dissipation when the tubes are run hard. If the amp were mine, I'd set the idling current to run as low as possible, cosistent with good tone from the amp. This will satisfy the guitar player in you, and help keep those great tubes healthy for a long time for you to enjoy.

There are some excellent tech articles and FAQs on this subject, posted on a few websites devoted to tubes and tone. If you haven't gotten to read some (and copy for future reference), you owe it to yourself to start. There are various ways to either directly measure the power tube idling current, or using an Ohm's Law algorithm, be able to infer what the current is by reading a voltage drop across a strategically placed resistor or using the output transformer primary as a shunt. You may already be versed in this stuff, so if you are, please don't take offense to the suggestion.

Just wondering, do your EL34s have a short base with a metal ring crimped around, or a typical brown or black full height bakelite skirt? The older versions with the metal ring were built to take abuse.

Doc

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