"Old " Hi-Fi

[joebog1]

For qualityten,
If you want to stay with an integrated amp, I include a version with built-in multi features, including a tape head amplifier, a central speaker output, and switching for five input sources.
My present amp ( also from RT&H ) has built-in phono, and I have busted one of those valves trying to cure the hum. Mind you, the phono stage is my design, and even enclosed in a 1.6mm thick steel separate enclosure under the chassis, and with the valves having screening cans fitted, AND DC heating, I still have hum. Its not overwhelming, but enough to be annoying when fully cranked and in between tracks. It outputs a staggering 7 watts RMS per channel, but with my speakers ( very sensitive by todays standards ) its very loud.

Although your present Heathkit amp is smaller with 6BM8 output bottles ( which are getting very rare ) it is immenently suitable with the iron you have to use 6V6, or 7C5 or even 6BW6 ( which is what my amp uses ) and with what the HT the Heathkit amp power transformer supplies, would still make a very nice amplifier. There are quite a few other valves that could be used with your output transformer impedances. Dont forget, that at that period in time Hammond did make very nice transformers!!. THey would still be paper insulated ( always a plus ) and varnished wire used. Rather than awful polyurethane insulation used today, along with scungy yellow polyester tape. (which I also use because nobody in Australia makes onion paper anymore )
You could of course use the origional 6BM8's, but use a different circuit ( RT&H also has several very nice amps using them ) which are available if you ask.

My own idea, which will use a separate preamp ( the subject initially of this thread ) and go with what I have to hand.

OK, I have given you enough to think about.

Joe

[joebog1]

last few pages,.

joe

[joebog1]

Being the slow-boy that I am, I forgot this excellent discussion.

Joe

[joebog1]

last two pagelets.

Joe

[joebog1]

A further note to Ed Dinning.
https://www.ebay.com.au/sch/i.html?_...0&LH_PrefLoc=2

[Ed_Dinning]

Hi Joe, they do look good quality, is that ceramic or nylon/ ptfe insulation.
Unfortunate that the shafts are not longer, not a problem at the front but nice to have it at the back so wafers can be "stacked" for stereo channels and kept quite well apart to reduce crosstalk

Ed

[whyperion]

I have a small interest in Stereo Records of the 1950s, they seem to have fallen out of general use until the later 1960s after about 1961, at least in the 7in format. I think for the UK one reason might have been purchase tax (plus the cost of two of everything for a stereo amplifier) and a lot of record players that were weighted to the mono standards that had only recently come into use after EMI and Decca reticence to produce microgrove recods until the mid 1950s in the first place. While I think Decca in the UK and RCA in America were recording masters in Stereo for some years - particularly Orchestral Works, others had to create new recordings.

Out of interest what does the "reverse" mean on the front panel

[Stevie342000]

Partly true Decca UK and EMI both had a back catalogue of stereo master tapes from about the same time as RCA in the US 1954. Stereo discs in UK were produced on the same scale as mono discs until 1967 when it was reversed it was mono that was pressed in smaller numbers.

EMI produced 7" singles from 1952, they were the last of the majors here to take it up. Decca produced stereo eps from the get go in 1958 as did EMI, Pye was the 1st to produce stereo discs in May 1958, they had a new purpose built studio set up for stereo from 1956, they as well as Decca UK used Ampex 300 Mulit-track 3 or 2 channel tape machines.

Post war there was no real market for most of it people could not afford to buy equipment so built there own and discs were expensive, purchase tax would not have helped either.


The reverse is swap Left to Right to right to left channels.....

[joebog1]

Ed,
Its definately high quality glazed ceramic. Its not high gloss, but more a very soft sandblast sort of finish. They are "so cheap " that I buy units with more wafers than I need, remove one or two and add spacers from origional Oak brand switches to give me the spacing I want. That way the long bolts are used to add distance between wafers. The spacing in my pics is made my small lands cast into the ceramic and it cannot be removed. My home meade electronic megger tests leakage as infinite on its 1000 volt range.
The contacts are also quite strong and are wiping both sides. I have only found break before make though. I havent found shorting wafers either.

Joe

[retailer]

Originally Posted by joebog1

Retailer, I have an "updated " version of the twin ten, entitled " a versatile 2X10W stereo amplifier.
Has lots of silly things like tape head and third speaker facilities. Also uses different voltage amp/phase splitter (7199's ).

Joe

I found the "versatile 2X10W stereo amplifier" on my RTV&H DVD - I'm not sure if I have any 7199's and I'm not keen to start buying them at the current crazy asking prices - plenty of so called "equivalents" though. The earlier Twin Ten interested me - it's not overly sensitive and the authors of article wax lyrical about it's performance.

[joebog1]

6BL8 are direct replacements. The 7199 is just a selected for audio low noise version.
Its a triode pentode for B/W TV sets. Its been used many times in Au. Especially in gain then phase splitter circuits for guitar amps. With a bit of fiddling some very low noise versions are easily found.
Check the Playmaster guitar amps for some ideas. Especially the 40 watt and 60 watt versions that run 6DQ6 TV line pentodes as output valves.
Goldentone amplifiers are a very near equivelent, highly desirable and are pulling very big prices if they havent been molested.
6BL8's are not yet a "discovery " so they are plentiful and cheap.

Joe

[joebog1]

As far as audio in general goes with RTV&H, or more correctly ANY construction article produced by them was always considered a bit special. I have already stated, and its common knowledge that it was all designed and built by engineers. They did have a few special blokes that could turn their hand to any design. If you are into amateur radio, some of their early designs are still in use.
LOTS of designs for SSB across all the bottom end bands. I dont "remember " anything much on two meters and above though.

Joe

[Robert Gribnau]

Originally Posted by joebog1

6BL8 are direct replacements. The 7199 is just a selected for audio low noise version.Joe

The 7199 and the 6BL8/ECF80 are not direct replacements of each other. Their pin-out differ and their characteristics are not identical.

But since the characteristics don't differ that much, they probably can replace each other in most audio applications when you would use an adapter.

[Stevie342000]

It is mentioned in the article that you need to swap out the wires to the pins if you change the valve from 7199 otherwise they are the same only the aforementioned is a lower noise version with different pin outs. I think it is or was in current production. Originals are not common it was used in Dynaco amps and was not used in the UK at all as far as I know.

[Robert Gribnau]

From the attached datasheets it follows that the characteristics of the 7199 and the 6BL8/ECF80 are not identical.

Triode section at Va = 100 V and Vg = -3 V:
7199: Ia is about 5 mA
6BL8/ECF80: Ia is about 9.5 mA

Pentode section at Va = Vg2 = 130 V and Vg1 = -2 V:
7199: Ia is about 6.5 mA
6BL8/ECF80: Ia is about 5 mA

Notes:
-The Philips datasheets for the ECF80 refers to the datasheets for the PCF80 for curves.
- I used the curves on page A of the datasheet for the PCF80 to graphically deduce Ia at Va = Vg2 = 130 V and Vg1 = -2 V.

[Robert Gribnau]

In the article (see the first attachment of post #22) it says that the 7199 basically is a selected version of the 6U8A, but with different pin-out.

The 6U8A however is not equivalent to the 6BL8/ECF80. The 6U8A is equivalent to the ECF82.

The datasheets of the 7199 and 6U8A/ECF82 confirm that those two types basically have the same characteristics.

[joebog1]

Thanks for that Robert. In both cases, that is, 7199 and 6U8 are very expensive and rare in Au. So, RTV&H used 6BL8 in essentially the same service as the aformentioned. I have built a number of the guitar amps using 6BL8's and they work very well indeed.

Sorry for the confusion all.

Joe