Audio Innovations Model 805 Valve Amplifier - UK Vintage Radio Repair and Restoration Discussion Forum

sennsai · 1st Apr 2019, 1:56 pm

I have this version of the 800 series. It's the typical 800 shape with the large black perforated cover, EL 34s but 8 ohm only. It's been upgraded with a large choke (in front of the mains transformer) taking place of one of the electrolytics.

Any information on it would be helpful as nothing comes up on searches.

Top Cap · 1st Apr 2019, 7:18 pm

Found this while web surfing, not sure if it is any use though?

Diabolical Artificer · 2nd Apr 2019, 6:28 am

Should be easy to trace out the schematic which would also show any mods done to it maybe. Any chance of some pics?

Andy.

snowman_al · 2nd Apr 2019, 7:13 am

Is it something that ''Border Patrol'' did to the 800?
I have a recollection of seeing an extra choke in one and it was attributed by the owner to be Border Patrol...
(Has it been fitted with a standby switch too?)
Yes pics and a list of the valves fitted would help.
Alan

GrimJosef · 2nd Apr 2019, 8:58 am

I contacted a friend of mine who worked on the Audio Innovations design team and he tells me that AI never put out a choke smoothed or choke input version of the 800. So this must be a third-party modification. Choke input was a feature of at least some Border Patrol power supply mods, but they often housed it, along with a new mains HT transformer as well, in a separate BP-branded case connected to the original amp by an umbilical.

Cheers,

GJ

sennsai · 2nd Apr 2019, 9:11 am

Top Cap- thanks for the clear diagram.

The right-hand switch is not connected.

Pics are here:

Diabolical Artificer · 3rd Apr 2019, 6:18 am

I'd try and move the big blue heater wires into the corner of the chassis or at least away from the sig input cable. The rest of the htr wiring is horrible; the layout in general could be better. Still, looks to have substantially built tfmr's.

Andy.

Robert Gribnau · 3rd Apr 2019, 7:04 am

In the diagram the upper half of the ECC82 is missing its grid resistor.

Robert

sennsai · 3rd Apr 2019, 1:54 pm

Thank you all for the constructive criticisms. Makes one wonder though at the cost of replacing those transformers, the choke and the rest. Anyhow it does sound well on my ELS 57s, although the TXs do get hot!

snowman_al · 3rd Apr 2019, 4:20 pm

I am not sure the transformers have been replaced.
You see pictures of very early Mark I Series 800s with exactly those 'open' transformers. (Also that single LS output rear chassis layout.)

The choke and extra switch are just as the reputed 'Border Patrol' mods I saw before.
Certainly it has been 'got at' at least a couple more times, some neat bits (Elna bypass caps?) and some not so neat as Andy says.

Do you have any history for it?
Alan

sennsai · 3rd Apr 2019, 8:27 pm

Sorry, no history, but I'll ask previous owner. I bought it with a faulty valve, replaced it and it then ran fine. The model plate on the rear is stamped Model 805, serial no. 919. I just assumed the TXs had been changed because they looked so clean.

Edward Huggins · 4th Apr 2019, 10:15 am

As with some Audio Innovations amplifiers, the Transformers were covered in a mesh metal cage, and this may have kept them clean - but it looks unlikely if that were the case on this version.

sennsai · 4th Apr 2019, 1:22 pm

Ah, it does have the black metal cover, perforated with small round holes rather than slots, it's just that I have been running the amp without it.

1st Apr 2019, 1:56 pm	#1
sennsai Tetrode Join Date: Jun 2016 Location: Worksop UK. Posts: 77	Audio Innovations Model 805 Valve Amplifier I have this version of the 800 series. It's the typical 800 shape with the large black perforated cover, EL 34s but 8 ohm only. It's been upgraded with a large choke (in front of the mains transformer) taking place of one of the electrolytics. Any information on it would be helpful as nothing comes up on searches.

1st Apr 2019, 7:18 pm	#2
Top Cap Octode Join Date: Mar 2006 Location: Watford, Hertfordshire, UK. Posts: 1,270	Re: Audio Innovations Model 805 Valve Amplifier Found this while web surfing, not sure if it is any use though? Attached Thumbnails __________________ Whether the Top Cap is Grid or Anode - touching it will give you a buzz either way!

2nd Apr 2019, 6:28 am	#3
Diabolical Artificer Dekatron Join Date: Jul 2009 Location: Sleaford, Lincs. UK. Posts: 7,661	Re: Audio Innovations Model 805 Valve Amplifier Should be easy to trace out the schematic which would also show any mods done to it maybe. Any chance of some pics? Andy. __________________ Curiosity hasn't killed this cat...so far.

2nd Apr 2019, 7:13 am	#4
snowman_al Octode Join Date: Dec 2018 Location: Llandeilo, West Wales, UK. Posts: 1,092	Re: Audio Innovations Model 805 Valve Amplifier Is it something that ''Border Patrol'' did to the 800? I have a recollection of seeing an extra choke in one and it was attributed by the owner to be Border Patrol... (Has it been fitted with a standby switch too?) Yes pics and a list of the valves fitted would help. Alan __________________ Never Leave Well Enough Alone...

2nd Apr 2019, 8:58 am	#5
GrimJosef Dekatron Join Date: Sep 2007 Location: Oxfordshire, UK. Posts: 4,311	Re: Audio Innovations Model 805 Valve Amplifier I contacted a friend of mine who worked on the Audio Innovations design team and he tells me that AI never put out a choke smoothed or choke input version of the 800. So this must be a third-party modification. Choke input was a feature of at least some Border Patrol power supply mods, but they often housed it, along with a new mains HT transformer as well, in a separate BP-branded case connected to the original amp by an umbilical. Cheers, GJ __________________ http://www.ampregen.com

2nd Apr 2019, 9:11 am	#6
sennsai Tetrode Join Date: Jun 2016 Location: Worksop UK. Posts: 77	Re: Audio Innovations Model 805 Valve Amplifier Top Cap- thanks for the clear diagram. The right-hand switch is not connected. Pics are here: Attached Thumbnails

3rd Apr 2019, 6:18 am	#7
Diabolical Artificer Dekatron Join Date: Jul 2009 Location: Sleaford, Lincs. UK. Posts: 7,661	Re: Audio Innovations Model 805 Valve Amplifier I'd try and move the big blue heater wires into the corner of the chassis or at least away from the sig input cable. The rest of the htr wiring is horrible; the layout in general could be better. Still, looks to have substantially built tfmr's. Andy. __________________ Curiosity hasn't killed this cat...so far.

3rd Apr 2019, 7:04 am	#8
Robert Gribnau Heptode Join Date: May 2017 Location: Konongo, Ghana Posts: 514	Re: Audio Innovations Model 805 Valve Amplifier In the diagram the upper half of the ECC82 is missing its grid resistor. Robert

3rd Apr 2019, 1:54 pm	#9
sennsai Tetrode Join Date: Jun 2016 Location: Worksop UK. Posts: 77	Re: Audio Innovations Model 805 Valve Amplifier Thank you all for the constructive criticisms. Makes one wonder though at the cost of replacing those transformers, the choke and the rest. Anyhow it does sound well on my ELS 57s, although the TXs do get hot!

3rd Apr 2019, 4:20 pm	#10
snowman_al Octode Join Date: Dec 2018 Location: Llandeilo, West Wales, UK. Posts: 1,092	Re: Audio Innovations Model 805 Valve Amplifier I am not sure the transformers have been replaced. You see pictures of very early Mark I Series 800s with exactly those 'open' transformers. (Also that single LS output rear chassis layout.) The choke and extra switch are just as the reputed 'Border Patrol' mods I saw before. Certainly it has been 'got at' at least a couple more times, some neat bits (Elna bypass caps?) and some not so neat as Andy says. Do you have any history for it? Alan __________________ Never Leave Well Enough Alone...

3rd Apr 2019, 8:27 pm	#11
sennsai Tetrode Join Date: Jun 2016 Location: Worksop UK. Posts: 77	Re: Audio Innovations Model 805 Valve Amplifier Sorry, no history, but I'll ask previous owner. I bought it with a faulty valve, replaced it and it then ran fine. The model plate on the rear is stamped Model 805, serial no. 919. I just assumed the TXs had been changed because they looked so clean.

4th Apr 2019, 10:15 am	#12
Edward Huggins Dekatron Join Date: Sep 2015 Location: Southwold, Suffolk, UK. Posts: 8,327	Re: Audio Innovations Model 805 Valve Amplifier As with some Audio Innovations amplifiers, the Transformers were covered in a mesh metal cage, and this may have kept them clean - but it looks unlikely if that were the case on this version. __________________ Edward.

4th Apr 2019, 1:22 pm	#13
sennsai Tetrode Join Date: Jun 2016 Location: Worksop UK. Posts: 77	Re: Audio Innovations Model 805 Valve Amplifier Ah, it does have the black metal cover, perforated with small round holes rather than slots, it's just that I have been running the amp without it.