BHK Mono first listen


#41

when the package with the test CD arrived, it included the user manual. I scanned the manual and it said that the BHK would self-adjust tube filament voltages to accommodate various tube types automatically. Is there a list of approved tube types? It didn’t mention what was allowed. I didn’t look close enough, but I’ll check again to see if there was a recommended tube.

–SSW


#42
Streets Still Works said when the package with the test CD arrived, it included the user manual. I scanned the manual and it said that the BHK would self-adjust tube filament voltages to accommodate various tube types automatically. Is there a list of approved tube types? It didn't mention what was allowed. I didn't look close enough, but I'll check again to see if there was a recommended tube.

–SSW


We shipped it with the recommended tubes pre-installed for you tongue-wink_gif

The Gold Lions were the winner to both Paul and Arnie’s ears against a pretty wide array of tubes. Another set of tubes might sound better for your system - it all comes down to your ears and your gear - but the Gold Lions are a great starting point.

If you want to start rolling tubes for the BHK, anything 6922 pin compatible “won’t blow up,” as engineering put it.


#43
Streets Still Works said I scanned the manual and it said that the BHK would self-adjust tube filament voltages to accommodate various tube types automatically.
It appears it is not filament voltage. It is bias.

From the manual:

“If you wish to experiment with different tubes, you may use most 6 or 7 Series triode without changing the bias, which is adjusted automatically.”


#44

A list would be very helpful. I don’t know which tubes are considered “pin compatible.” For example, 6H30P tubes have the same number and size pins but I doubt it would work (some vendors expressly state it is not a drop-in replacement for a 6922 even though there are some similarities, including presumably being 6 volt). I don’t know if the pins are assigned the same functions (i.e., what the internal wiring is) for that tube or other tubes.


#45
Scott Schroeder said

If you want to start rolling tubes for the BHK, anything 6922 pin compatible “won’t blow up,” as engineering put it.


I received some 6922 / Telefunken E88CC tubes from Kevin Deal at Upscale Audio late last week in anticipation of the BHK mono arrivals. These are essentially NOS Telefunkens that were made in 1968 and have rave reviews in terms of the microphonics, etc. (not a bad price point either, incidentally for those maybe wanting to roll some NOS tubes) I plan to critically listen to the gold lions and roll the E88CC’s and report on both.

#46

I am using those Telefunken tubes from Kevin in my SP-10 preamp now. Had also planned to roll them into the BHK. They added life/real sound to the SP-10. Going to get some Gold lions to use in preamp as another option.


#47
st50maint said
Streets Still Works said I scanned the manual and it said that the BHK would self-adjust tube filament voltages to accommodate various tube types automatically.

It appears it is not filament voltage. It is bias.

From the manual:

"If you wish to experiment with different tubes, you may use most 6 or 7 Series triode without changing the bias, which is adjusted automatically."


Good catch, it is bias not filament voltage. I’m still a tube noob, so I’ll have to defer to others with more experience (Bascom, get in here!), on what fits the bill for being pin compatible. I’d say avoid rolling 6H30P tubes until we know for sure.

#48

The manual says “most 6 or 7 Series triodes” should work. I’m holding off until I know what “most” means and what is included in 6 or 7 series triodes. I suspect it’s not every small signal tube that starts with a 6 or 7 and has nine pins but I don’t know enough about it to be comfortable just dropping in tubes. I’m not planning on trying anything other than 6922s and equivalents (like 6DJ8). For that matter, I’m pretty happy with the Gold Lions (I use them in my second system) and it’s a pain to pull the amp out of the rack to get to the tubes so I may just leave things as they are.


#49

The 6922 is a military grade of the more commonly available 6DJ8 tube. The 7308 is another high grade direct substitute for the 6DJ8, so any of these tube types should be suitable for the circuit as designed. Of course Bascom can please confirm this and add any other possibilities.


#50
stevem2 said A list would be very helpful. I don't know which tubes are considered "pin compatible." For example, 6H30P tubes have the same number and size pins but I doubt it would work (some vendors expressly state it is not a drop-in replacement for a 6922 even though there are some similarities, including presumably being 6 volt). I don't know if the pins are assigned the same functions (i.e., what the internal wiring is) for that tube or other tubes.
BHK Here: Although a 6H30P is pin compatible with the 6922 and variants, the 6H30P draws about three times the heater current and would likely take the heater regulators out of regulation and overheat them. Therefore not a good idea to try ;-(

#51
stevem2 said The manual says "most 6 or 7 Series triodes" should work. I'm holding off until I know what "most" means and what is included in 6 or 7 series triodes. I suspect it's not every small signal tube that starts with a 6 or 7 and has nine pins but I don't know enough about it to be comfortable just dropping in tubes. I'm not planning on trying anything other than 6922s and equivalents (like 6DJ8). For that matter, I'm pretty happy with the Gold Lions (I use them in my second system) and it's a pain to pull the amp out of the rack to get to the tubes so I may just leave things as they are.
BHK Here: I believe this means that 7DJ8/PCC88 tubes will work. I don't know about any other 7V series triodes that would work. One could peruse an old RCA tube manual to look for others.

#52
Scott Schroeder said
st50maint said
Streets Still Works said I scanned the manual and it said that the BHK would self-adjust tube filament voltages to accommodate various tube types automatically.

It appears it is not filament voltage. It is bias.

From the manual:

“If you wish to experiment with different tubes, you may use most 6 or 7 Series triode without changing the bias, which is adjusted automatically.”

Good catch, it is bias not filament voltage. I’m still a tube noob, so I’ll have to defer to others with more experience (Bascom, get in here!), on what fits the bill for being pin compatible. I’d say avoid rolling 6H30P tubes until we know for sure.


Bascom getting in here: I have just recently said that 6H30’s are not a good idea because of the much greater heater current requirement. The tube input stage has a constant current source that keeps the plate current the same for different gain triodes. the grid to cathode voltage or bias will adjust to make this so. In effect the operating point regarding the resultant plate voltage on the tubes will be the same.

#53

@BHK: Any update as to the mono testing? (very hopefully asking)


#54

Thanks Bascom. That’s very helpful. I’m not surprised that 7DJ8s would work as they seem to be a minor variant on 6DJ8s. I’d suggest revising the manual so the statement does not seem so broad.


#55
patentpending said @BHK: Any update as to the mono testing? (very hopefully asking)
Yes, some things of interest. Someone on the forums had asked about IM distortion. I set up the CCIF IM test where 19 & 20 kHz tones are mixed together in equal amplitude. The test looks for the first order difference tone of 1 kHz. I tested at 10 & 50 W so far with distortions at 1W & 50W of -95 and -90 dB. Another thing much to my surprise, and it may be measurement error, the damping factor of the mono was quite a bit more than twice what I measured on my Sig 250 at about 640 at low frequencies. The Sig 250 was more like 140 but over a wider frequency range. I will probably do these over again. I will pass on my measurements to PS Audio soon and some of them will be included for more complete data on the amps.

#56
stevem2 said A list would be very helpful. I don't know which tubes are considered "pin compatible." For example, 6H30P tubes have the same number and size pins but I doubt it would work (some vendors expressly state it is not a drop-in replacement for a 6922 even though there are some similarities, including presumably being 6 volt). I don't know if the pins are assigned the same functions (i.e., what the internal wiring is) for that tube or other tubes.
I'm inclined to agree with you that a list would be helpful. So I present to you the List of Tubes that are Okay to Stick in the BHK 250 and 300!

Tubes that are okay:

•6DJ8/6922
•7308
•CV2493
•7DJ8/PCC88
•6H23

Tubes that are NOT okay:

•6H30

So far that’s it. As we discover more, I will let you guys know.


#57

Thanks Scott! Much appreciated.


#58

If it were me, I’d try 7308s. Those are my favorite of those tube types.


#59
BHK said Someone on the forums had asked about IM distortion.
Another thing much to my surprise, and it may be measurement error, the damping factor of the mono was quite a bit more than twice what I measured on my Sig 250 at about 640 at low frequencies. The Sig 250 was more like 140 but over a wider frequency range. I will probably do these over again. I will pass on my measurements to PS Audio soon and some of them will be included for more complete data on the amps.
Thanks Bascom, that was me, but post Paul's interview with you.

I had been asking about Slew rates pre-interview, but now understand Damping factor / output impedance to be more relevant (beyond a minimum slew rate).

Interesting result, a touch more than four times (2 squared ?) the 250. Is that per Mono ? I guess it would be per Mono - hard to test anything else without including Speakers in the load calculation & that wouldn’t seem to be a standardised test (CCIF test mentioned).

Interesting, beyond the result itself, once confirmed, as it may play into the Parallel amplification line of inquiry that seems to be Paul’s hunch on why the Mono amaze him.

Wonder if you have any insights into what may be occurring, mathematically, or intuitively? EDIT : or perhaps combining both concepts… electrically (a.k.a. the dark art of RF).

I’ve been playing with two sets of speakers off monoblocks, & I’m wondering if at a basic level whether two signal paths within the mono is similar, but doubt this guess is helpful as I recall reading the BHK design is fully balanced from input to output.

Thanks again. I’m still amazed (delighted) that you are available to discuss your creation here. Thanks for your patience !


#60
Green Machine said

Interesting, beyond the result itself, once confirmed, as it may play into the Parallel amplification line of inquiry that seems to be Paul’s hunch on why the Mono amaze him.

@BHK: I'm dying to know if you confirmed that damping factor measurement on retest. 640 would be off the charts...