Retubing Orange AD140HTC Suggestions

[Azmedian]

Just looking to have my amp serviced & was looking at the options I might have if retube is warrented

Stock Tubes ECC83 & EL34

Any suggestions for different tubes Hard Rock tones can always use a pedal to push it

Anyone know if I can put KT88's In ??

Looking to keep the amp healthy

Any advise is appreciated

[Stevem]

What are you looking for, more clean head room before the output stage clips if you’re even pushing a 140 watt amp that loud?

Opening your wallet wider for KT88s will give you a bit more clean head room, but not anymore wattage.

Also the amp will need to get rebiased for the 88s and the amp may not have enough spare bias voltage to contain the 88s from red plating, and this may it may not be able to be delt with.

If you want to avoid all of this then if you live in the US order up a set of EL34L tubes from Groovetubes in a number 10 rating .

If your in Europe then get on the Watford valves site, as I bet they can help you also, and even with recommendations for preamp tubes just as Euro tubes here in the states can.

[nuke]

While many will wax poetic about the fine floral and mineral hints of particular tubes, the truth is replacing a properly functioning 12AX7/ECC83 with another properly functioning 12AX7/ECC83 from a different brand, will yield nearly identical results. That's the whole behind standardized part numbers. There are occasionally rare exceptions where an OEM selected a particular vendor because they wanted to operate at some point outside the tube's datasheet.

Your amplifier is pretty much standard circuitry, with nothing running outside or near the electrical limits of any ordinary 12AX7/ECC83 tube.

I'll also say that in my experience with guitarists, some of whom wear their tube sockets out habitually rolling tubes, is that a lot of the differences sensed are imaginary.

For preamp tubes, if it is the right type, if it isn't microphonic, noisy, or making excess hum, and an in circuit evaluation says it is making the expected gain and behaving properly, then there's really no reason to change it.

On the KT88 question, the KT88 draws more heater current, about 8% more, which is likely OK. The other thing is whether the bias supply is capable of producing enough negative voltage to bias the KT88. That's something to evaluate with the amplifier in hand. In general, the EL34's will reach power tube distortion earlier, the KT88's will stay cleaner to higher drive levels. But if you're not operating with power amp clipping, then it likely won't make a whole lot of difference. A 4xEL34 amplifier will make around 100 watts pretty cleanly and that's really loud. So if you're not playing large stages and outdoor arenas, you're probably getting all the drive from the preamps.

[Stevem]

One thing I would like to add about preamp tubes is this .

The section of a preamp tube that drives a tone stack DOES have an effect on how the amp sounds and responds to your playing.

If a 12ax7 or ECC83 fully meets its design specifications then either the A or B side will be able to output 1.2 ma.

The closer to design specifications the tube is that drives your tone stack then the less signal loss there will be thru the tone stack and the tone stack will have a wider range of control in regards to its knobs when the knobs are adding resistance resistance to the circuit, IE closing down .

If you have a two channel amp with two different tone stacks then depending on how the amp is designed the amp may have two tubes that should be well tested and rated for meeting design specifications.

In a very real way I find that the smaller a tubes plate structure is which certainly helps it to be less microphonic then the less the chances are that the tube will meet design specifications.

Also the larger the size of a tubes plate structure, then in general it will last longer and many times a lot longer especially if you have invested in new old stock tubes or run the new manufacture big plate tubes made by JJ electronics and sold here in the US by Euro tubes on the west coast.

Also preamp tubes in any that are called on to drive the outputs ( the PI tube ) are also being called upon to output a lot of current and this can eat up some new manufacture tubes pretty darn fast.

Just try using a China made 12ax7b for a PI tube and take note of how fast the tube degrades.

Metal players rely on basically on all cascading preamp distortion and don’t care or need for much dynamic range.

A preamp tube that test out in the 85% Gm range will 95 percent of the time not need a well tested preamp tube that meets its full design specifications.

[Roe]

schematic

[nuke]

There's nothing really going on special in this amp, it's pretty vanilla circuit-wise. The phase inverters have a large tail resistor, and the voltage at the cathode will be about 67V above ground, meaning the heater-cathode voltage might bear some attention That voltage with respect to ground is well within the ECC83/12AX7 spec sheet. However, some modern made tubes seem vulnerable to H-K voltage differential.

I've not found a big difference between tube brands in the preamp section feeding a standard tone stack configuration, such as in this design. As long as the tube is within speck and working properly it should sound more or less like any other. But, use whatever seems good to you.