8BQ5 tubes

[jonfrum]

I'm wondering where these tubes were originally used. I assume they
were in radios, but I've never seen a schematic using them.

[Martin Crossley]

Post by jonfrum
I'm wondering where these tubes were originally used. I assume they
were in radios, but I've never seen a schematic using them.

The European version (EL84) superseded the EL41 and was very
common indeed in better quality sets from the mid 50s, which co-incided
with the start of FM broadcasting in the UK and also widely used in record
players,
(A search on www.radiomuseum.org shows over 500 models.)
They were also popular in Hi-Fi amps like the Mullard 5-10 design
and the Heathkit MA12.
Martin.

[John Goller, k9uwa /W4 Snowbird]

In article <4410c2f1$0$9233$***@ptn-nntp-reader01.plus.net>,
***@g8uwm.NOSPAMabelgratis.net says...
think U didn't read the number right ... poster said 8 BQ5
most likely same tube as 6bq5 with 8 volt filament

John

[Martin Crossley]

Post by John Goller, k9uwa /W4 Snowbird
think U didn't read the number right ... poster said 8 BQ5
most likely same tube as 6bq5 with 8 volt filament
John

Yes, you are quite right.
I have text at largest, so messages are easy to read,
but in OE, the titles stay small.
Never heard of the 8BQ5!
I know the PL84 (15CW5) and UL84 (45B5),
but that's no help...
Sorry.
Martin

[Stephen Wild]

I am assuming you actually meant 8BQ5, not 6BQ5 as the earlier poster did.
My RCA tube manual does indeed list an 8BQ5 and a 10BQ5.

My assumption is that these two 6BQ5 variants were for use in series string
television sets - I know for a fact that the 0.45 Amp rating of the 10BQ5
was common in inexpensive black and white sets.

The 8BQ5 list as being an 0.60 Amp which I surmise may have been used in
colour televisions - but I am not a TV expert and may be incorrect here.

In any case, I am in agreement that you would not see them in radio or
amplifier designs - the voltage rating is too oddball for transfomer
operated equipment, and the 0.6 A rating was not used to my knowledge in
series string radio sets - again, I may stand to be corrected here.

Post by jonfrum
I'm wondering where these tubes were originally used. I assume they
were in radios, but I've never seen a schematic using them.

[Martin Crossley]

Post by Stephen Wild
I am assuming you actually meant 8BQ5, not 6BQ5 as the earlier poster did.

Oops!
I'll have to get a better monitor or some newer eyes.
Martin.

[jonfrum]

I'm putting them into a guitar amplifier, so I'll be using an 8V
filament transformer. Same tube as 6BQ5, at a fraction of the price.

[Bob]

You can use a 12.6V transformer if you use an unfiltered rectifier
diode in series with the 8BQ5. Same power delivered to the 8BQ5 that
way vs a 12BQ5 (if they existed) without diode.

[Terry]

Post by Bob
You can use a 12.6V transformer if you use an unfiltered rectifier
diode in series with the 8BQ5. Same power delivered to the 8BQ5 that
way vs a 12BQ5 (if they existed) without diode.

Hey that's interesting, and ingenious. Presuming you mean?
V squared divided by R = watts as follows.
1) At 8 volts; (8 x 8)/R = 64/R
2) At 12.6v; (0.5* x 12.6 x 12.6)/R = 0.5 x 159/R = 79/R
* denoting half wave.
And.
3) At 12v (0.5 x 12 x 12/R = 72/R
NB. The rated heater of an 8BQ5 from various sources is 8 volts at 0.6 amps.
R = 8/0.6 = 13/3 ohms (hot).

I tried this once using a voltage 'twice' the rated voltage of the tube
(well it was actually a lamp!) in series with a diode, without a filter
capacitor. It blew the smithereens out of the lamp filament!

4) Hmm! (0.5 x 2v x 2v)/R = 2v/R. Yes that would do it. Didn't even act
like a photoflood with a shorter lifespan. Just flash, 'poof'; lamp flashed
once and that was it! Expensive bulb too!

BTW have operated a single tube heater in series with a capacitor, on AC
mains.
Capacitive reactance formula = one all divided by (two pi x freq. x C
farads)

A one mfd capacitor having an AC impedance at 60 cycles of around 2800 ohms
(reactive).
Thus a 3 to 4 mfd cap having a reactance of around 930 to 700 ohms will pass
somewhere between 0.13 and 0.16 amps at 115 to 120 volts AC.

The R component of this what is really a vector problem is so small (often
less than say 0.5%) it can be ignored.

At 50 hertz (where I first tried this as a penniless schoolboy) reactance is
3,300 ohms and with 230 volts mains a 2 mfd cap will pass about 0.14 amps.

Since many 12 (12.6) volt tubes require 0.15 amps (compared to their 6.3v
brethren) this is occasionally a quick way to 'fire up' such a tube without
a transformer!

Of course if the cap blows because of the peak voltages the tube goes too!
But as experiment or an emergency!

So 0.6a for a couple of 8BQ5s could be possible with say a 10 to 12 mfd.
cap, of suitable AC rating. But that's getting physically rather large for
such a cap even if one has a stock of ex-telephone caps. production tested
to 2 KV static DC!

[Bob]

"Hey that's interesting, and ingenious. Presuming you mean?
V squared divided by R = watts as follows.
1) At 8 volts; (8 x 8)/R = 64/R
2) At 12.6v; (0.5* x 12.6 x 12.6)/R = 0.5 x 159/R = 79/R
* denoting half wave.
And.
3) At 12v (0.5 x 12 x 12/R = 72/R "

That's it. You can use this same trick to operate a series string that
adds up to 84V with the diode off of 120VAC.

Another approach is to use a 24V transformer and 3 8BQ5s in series. Or
2 of them and 8V worth of selected 600ma TV tubes for drivers and audio
processing.

[John Goller, k9uwa /W4 Snowbird]

Post by Bob
"Hey that's interesting, and ingenious. Presuming you mean?
V squared divided by R = watts as follows.
1) At 8 volts; (8 x 8)/R = 64/R
2) At 12.6v; (0.5* x 12.6 x 12.6)/R = 0.5 x 159/R = 79/R
* denoting half wave.
And.
3) At 12v (0.5 x 12 x 12/R = 72/R "
That's it. You can use this same trick to operate a series string that
adds up to 84V with the diode off of 120VAC.
Another approach is to use a 24V transformer and 3 8BQ5s in series. Or
2 of them and 8V worth of selected 600ma TV tubes for drivers and audio
processing.

surplus electronics stores have all sorts of small control voltage
transformers... usually 2 to 4 bucks each range.. pretty easy to
get 15 & 16 volt ones and 18 volt ones... also of course 24 volt
is common ...
John

[Tom Bavis]

Post by Bob
You can use a 12.6V transformer if you use an unfiltered rectifier
diode in series with the 8BQ5. Same power delivered to the 8BQ5 that
way vs a 12BQ5 (if they existed) without diode.

A possible refinement: use 12VAC and series connect them, shunted
with back-to-back diodes. Like this:

-+--/\---+-----/\---+--
| | |
+--->|---+-----|<---+

If you run out of 8BQ5s, clip the diodes to use 6BQ5s

[Stein-Olav Lund]

Post by jonfrum
I'm putting them into a guitar amplifier, so I'll be using an 8V
filament transformer. Same tube as 6BQ5, at a fraction of the price.

Price may be an important factor, and for a new design I agree fully
with you.
EL84/6BQ5 is easy however, still mfd 'everywhere'..
Situation is worse with the ECL86/6GW8, no longer made, much used and
sought after..
If you can manage to get 13V heater voltage you can use the PCL86/14GW8
used in most European b/w colour TVs sound outputs.
The PCL86 isn't much used nowadays and prices are a fraction of that of
ECL86..

Stein

[Ken Scharf]

Post by Stephen Wild
I am assuming you actually meant 8BQ5, not 6BQ5 as the earlier poster did.
My RCA tube manual does indeed list an 8BQ5 and a 10BQ5.
My assumption is that these two 6BQ5 variants were for use in series string
television sets - I know for a fact that the 0.45 Amp rating of the 10BQ5
was common in inexpensive black and white sets.
The 8BQ5 list as being an 0.60 Amp which I surmise may have been used in
colour televisions - but I am not a TV expert and may be incorrect here.

A quick scan of an old RCA receiving tube manual shows B&W picture tubes
were made with BOTH 450ma and 600ma heaters, the lowest current drawn
by color crt heaters was 900ma and up to 1800ma. So the 8BQ5 with
a 600ma heater current would be right for about half of the B&W sets,
with the other half having a 450ma heater string.

In general the 70 and 90 degree B&W crt's were 600ma and the 110's
could be either 450 or 600ma. No fast rules there.

[Mark Oppat]

TV sets. Where most series filiment tubes lived. If you are savvy, you can
make a lot of guitar amps or other audio amps, using these twins to the 6v
versions. God knows there are billions of them , NOS, in storage still at
cheap prices!

Mark Oppat

Post by jonfrum
I'm wondering where these tubes were originally used. I assume they
were in radios, but I've never seen a schematic using them.

[Omer Suleimanagich]

Could you add a dropping resistor and use these tubes as EL84's?

Omer

Post by Mark Oppat
TV sets. Where most series filiment tubes lived. If you are savvy, you can
make a lot of guitar amps or other audio amps, using these twins to the 6v
versions. God knows there are billions of them , NOS, in storage still at
cheap prices!
Mark Oppat

Post by jonfrum
I'm wondering where these tubes were originally used. I assume they
were in radios, but I've never seen a schematic using them.

[Omer Suleimanagich]

I meant, something to raise the voltage?


Take a look at the RMorg site on this topic:
http://www.radiomuseum.org/forum/pcl86.html?thread_id=101513

Omer

Post by Omer Suleimanagich
Could you add a dropping resistor and use these tubes as EL84's?
Omer

Post by Mark Oppat
TV sets. Where most series filiment tubes lived. If you are savvy, you can
make a lot of guitar amps or other audio amps, using these twins to the 6v
versions. God knows there are billions of them , NOS, in storage still at
cheap prices!
Mark Oppat

Post by jonfrum
I'm wondering where these tubes were originally used. I assume they
were in radios, but I've never seen a schematic using them.

[m***@panic.xx.tudelft.nl]

Post by jonfrum
I'm wondering where these tubes were originally used. I assume they
were in radios, but I've never seen a schematic using them.

Equivalent to the European XL84, 600mA filament. European TV sets mostly
used P series (300mA filament). I'd guess TV-sets designed for 110V
operation would have used X series tubes.

-
Met vriendelijke groet,

Maarten Bakker.