Hiwatt 200 DR201 pre-launch checklist

[TomCarlos]

Team MEF...

Yup, another Hiwatt on the bench. And most of you know me, I am NOT the expert here. This one looks a bit intimidating, especially one with original six tubes!!

This amp has not been turned on for a couple years. Before doing so, I want to conduct a pre-launch check.

Hiwatt 200 - DR201 schematic: https://el34world.com/charts/Schematics/files/Hiwatt/Hiwatt_200w_dr201.pdf (also attached).

I am not familiar with the EL34s, but they look like 6L6 connected in a Pentode mode. One of my first checks is the tubes. They all show a health emission reading but one tube appears to have some Grid Leakage. My first question is, knowing that all other tubes have a reading to the far left of the meter, would you insert tube #5 just for testing, knowing the Grid Leakage reading is in the questionable area?

I will checking the Grid and Screen resistors and the Power Supply and Bias Caps.

Q2 - Does anyone have any idea how much current this amp would draw at idle?

I am off to read the other posts on this site for the same amp, including this one: "Hiwatt 200 (DR201) bias pot + general questions"

Thanks !!

Hiwatt_200w_dr201.pdf

[g1]

I have no answer to your questions, but that sure does not look like an EL34 to me.

[TomCarlos]

There are no markings on the tubes... could be a KT-88?

[g1]

There are no markings on the tubes... could be a KT-88?

That's kind of what I was thinking, or 6550. As long as they are all the same and it was functional when put away, should not be a problem.
I was more thinking that if it were an oddball compared to the others, you might get a different reading on the tester.
But with grid leakage, best to not use it I think.
Maybe test with 4 power tubes instead of six.

[drewl]

Tung Sol or maybe Genelex 6550, old!

[TomCarlos]

G1 and Drewl, you are probably right. Those might be 6550 tubes. I just don't know enough about them to say one way or another and there are no markings on the tubes.

So, I checked caps, screen resistors, grid resistors, plate resistors, anything touching a tube - all good. I checked the Bias voltage, -42 volts. Close enough. As G1 suggested, 4 tubes only. The amp powers up and passes a signal. It is relatively clean. I am hesitant to "take it to the limit" at this point in time. I'm just happy the amp works and I am sure my bud will feel the same.

I do need to replace the two Normal input jacks, they are worn. So for the initial power on, we will call this one a success.

Now then.... those output tubes.... what to suggest for a replacement. Maybe the owner should stick to the original design of EL34s.

[Jon Snell]

If it is a real HiWatt, you firstly need six EL34s otherwise the bias voltage will be wrong. DO NOT USE Chinesium valves, they are not good enough and may flash over inside with the 700 volts HT! I always fit Svetlana Winged "C". Expensive but you won't repace them again for at least 10 years of gigging.
If it has not been powered up for a long while, bring the mains up slowly with no valves in it and look and listen for any odd noises. It may take 15 minutes to reform those old electrolytics but there is no need to replace them as long as they have no signs of issues.
When the main HT readhes around 650 volts, let it sit there for half an hour and monitor the main smoothing capacitors for signs of near death.

If all OK, power it down and wait 10 minutes to allow the capacitors to discharge then fit the valves and power it up, with speakers connected.
Look for any obvious fault; anode load resistors particularly the 82k and 91k phase splitter load resistors and, yes, it must be 91k.
Lovelly old English amplifiers.
If it is not original, (5881s look suspect), either put it back to how it was built or good luck with repairing something.

[Helmholtz]

I always fit Svetlana Winged "C". Expensive but you won't repace them again for at least 10 years of gigging.
.

AFAIK, the Svetlana Winged "C" EL34 production was closed in 2012.

[TomCarlos]

Thank you Helmholtz and Jon....

Yes, I did a slow power up before installing the tubes.

Some updates....

Serial Number: 10558, Most likely 1977 model

It would be a good idea to draw out the input jack connections for this amp. But you can see the resistors going across the four mono jacks. The grounds are all connected to a single point on the chassis.

The amp looks original. The Bias cap has been replaced, not sure about the Power Supply caps.

Someone previously installed a Post Phase Inverter Master Volume control. That has since been taken out and the amp appears to be wired back as original.

As reported earlier, one of the Jacks on the Normal inputs is damaged. The spring is not allowing the contact to lift properly when the plug is inserted.

For testing, I am running only 4 tubes - whatever type they are. The output level is low but it could be the output tubes, preamp tubes, not my big concern at this point in time. I am merely trying to survey the condition of the amp.

Voltages as follows:

Pin 1 - Suppressor Grid - 0 volts, connected to chassis
Pin 2 to Pin 7, Heaters, 6.4 volts ac
Pin 3 - Plate, 675 volts
Pin 4 - Screen Grid, 370 volts
Pin 5 - Control Grid, -41 volts
Pin 6 - Normally No Connection, but they are tied together and used as common connection point for the 1K screen resistors that connect to pin 4
Pin 8 - Cathode - 0 volts, connected to chassis

Using a bias probe, again I am running four unknown tubes....

Tube 6
Plate voltage, 675 volts,
Cathode current, 53ma

Tube 1`
Plate voltage, 675 volts,
Cathode current, 45ma


If these tubes are 6550 @ 42 watts, that says the tube is running at approx 75% to 80% power dissipation

If these tubes are 6550 @ 35 watts, that says the tube is running at approx 90% power dissipation

But at least we know this is 675 volts on the plates.

[Jon Snell]

AFAIK, the Svetlana Winged "C" EL34 production was closed in 2012.

I have some matched quads left in stock that I purchased in 1999/2000.

[Jon Snell]

I would say, without a doubt, it was built in 1981 judging by the RS capacitors that are dated the 26th week of 1980, if original.
For those that do not know, RS Components originally known as RadioSpares back in the 60s purchased components from known good sources and re branded them. Later, as in your photo, the manufacturer was tasked to use the RS brand logo on the components.

RS is still a well respected supplier of good quality components, covering Europe and Great Britain.

[Pedro Vecino]

If these tubes are 6550 @ 42 watts, that says the tube is running at approx 75% to 80% power dissipation

If these tubes are 6550 @ 35 watts, that says the tube is running at approx 90% power dissipation

I have compared the image of the tube (what little can be seen of it) and it cannot be a modern Tung Sol 6550. The contour of the micas is very different.
Could be a tube they call KT88/98 (Shuguang)

https://www.thetubestore.com/shuguang-kt88-98

I am afraid that you will have to make a more conservative bias adjustment than 45 and 53mA (although when installing the other two it drops a bit). I see in the schematic that the original bias circuit does not give more of itself, as it happens with the DR103. In these circumstances I usually use a voltage doubler prior to an adjustable circuit.

[TomCarlos]

Thank you Pedro.....

I recommended that the owner purchase new EL34s and we check the bias. If necessary, we'll tweak the bias circuitry. First things first.

Later today, after a bit more pot and tube socket cleaning, the amp was putting out adequate volume with the four tubes. We were using the 8 ohm tap. So I hope that four tubes into the OT and using the 8 ohm tap will be ok for low volume playing while we await the sextet tube set.

[mhuss]

Note that the older DR201s used 4 (original GEC) KT88s and the later ones (like you have) used 6 EL34s - I believe both are approximately the same, output impedance-wise, and both models used the same or equivalent OTs.

Cleaner schematics:
https://hiwatt.org/Schematics/DR_Pre4Input_v2.pdf (most likely?)
https://hiwatt.org/Schematics/DR_200wOutput6.pdf
https://hiwatt.org/Schematics/DR_200wPS.pdf

[TomCarlos]

Thank you Mark.... and I see your name on those diagrams. Much appreciated.